diff --git a/nonebot/adapters/_message.py b/nonebot/adapters/_message.py
index 57eaebaf..ffeb2bf5 100644
--- a/nonebot/adapters/_message.py
+++ b/nonebot/adapters/_message.py
@@ -14,27 +14,28 @@ from typing import (
     Tuple,
     Union,
     Generic,
-    Mapping,
     TypeVar,
     Iterable,
     Optional,
     overload,
 )
 
+from pydantic import parse_obj_as
+
 from ._template import MessageTemplate
 
 T = TypeVar("T")
-TMS = TypeVar("TMS", covariant=True)
+TMS = TypeVar("TMS", bound="MessageSegment")
 TM = TypeVar("TM", bound="Message")
 
 
 @dataclass
-class MessageSegment(Mapping, abc.ABC, Generic[TM]):
+class MessageSegment(abc.ABC, Generic[TM]):
     """消息段基类"""
 
     type: str
     """消息段类型"""
-    data: Dict[str, Any] = field(default_factory=lambda: {})
+    data: Dict[str, Any] = field(default_factory=dict)
     """消息段数据"""
 
     @classmethod
@@ -54,26 +55,26 @@ class MessageSegment(Mapping, abc.ABC, Generic[TM]):
     def __ne__(self: T, other: T) -> bool:
         return not self == other
 
-    def __add__(self, other: Union[str, Mapping, Iterable[Mapping]]) -> TM:
-        return self.get_message_class()(self) + other  # type: ignore
+    def __add__(self: TMS, other: Union[str, TMS, Iterable[TMS]]) -> TM:
+        return self.get_message_class()(self) + other
 
-    def __radd__(self, other: Union[str, Mapping, Iterable[Mapping]]) -> TM:
-        return self.get_message_class()(other) + self  # type: ignore
+    def __radd__(self: TMS, other: Union[str, TMS, Iterable[TMS]]) -> TM:
+        return self.get_message_class()(other) + self
 
-    def __getitem__(self, key: str):
-        return getattr(self, key)
+    @classmethod
+    def __get_validators__(cls):
+        yield cls._validate
 
-    def __setitem__(self, key: str, value: Any):
-        return setattr(self, key, value)
-
-    def __iter__(self):
-        yield from asdict(self).keys()
-
-    def __contains__(self, key: Any) -> bool:
-        return key in asdict(self).keys()
+    @classmethod
+    def _validate(cls, value):
+        if isinstance(value, cls):
+            return value
+        if not isinstance(value, dict):
+            raise ValueError(f"Expected dict for MessageSegment, got {type(value)}")
+        return cls(**value)
 
     def get(self, key: str, default: Any = None):
-        return getattr(self, key, default)
+        return asdict(self).get(key, default)
 
     def keys(self):
         return asdict(self).keys()
@@ -101,20 +102,20 @@ class Message(List[TMS], abc.ABC):
     """
 
     def __init__(
-        self: TM,
-        message: Union[str, None, Mapping, Iterable[Mapping], TMS, TM, Any] = None,
-        *args,
-        **kwargs,
+        self,
+        message: Union[str, None, Iterable[TMS], TMS] = None,
     ):
-        super().__init__(*args, **kwargs)
+        super().__init__()
         if message is None:
             return
-        elif isinstance(message, Message):
-            self.extend(message)
+        elif isinstance(message, str):
+            self.extend(self._construct(message))
         elif isinstance(message, MessageSegment):
             self.append(message)
+        elif isinstance(message, Iterable):
+            self.extend(message)
         else:
-            self.extend(self._construct(message))
+            self.extend(self._construct(message))  # pragma: no cover
 
     @classmethod
     def template(cls: Type[TM], format_string: Union[str, TM]) -> MessageTemplate[TM]:
@@ -154,7 +155,7 @@ class Message(List[TMS], abc.ABC):
         """获取消息段类型"""
         raise NotImplementedError
 
-    def __str__(self):
+    def __str__(self) -> str:
         return "".join(str(seg) for seg in self)
 
     @classmethod
@@ -163,51 +164,97 @@ class Message(List[TMS], abc.ABC):
 
     @classmethod
     def _validate(cls, value):
+        if isinstance(value, cls):
+            return value
+        elif isinstance(value, Message):
+            raise ValueError(f"Type {type(value)} can not be converted to {cls}")
+        elif isinstance(value, str):
+            pass
+        elif isinstance(value, dict):
+            value = parse_obj_as(cls.get_segment_class(), value)
+        elif isinstance(value, Iterable):
+            value = [parse_obj_as(cls.get_segment_class(), v) for v in value]
+        else:
+            raise ValueError(
+                f"Expected str, dict or iterable for Message, got {type(value)}"
+            )
         return cls(value)
 
     @staticmethod
     @abc.abstractmethod
-    def _construct(msg: Union[str, Mapping, Iterable[Mapping], Any]) -> Iterable[TMS]:
+    def _construct(msg: str) -> Iterable[TMS]:
         """构造消息数组"""
         raise NotImplementedError
 
-    def __add__(self: TM, other: Union[str, Mapping, Iterable[Mapping]]) -> TM:
+    def __add__(self: TM, other: Union[str, TMS, Iterable[TMS]]) -> TM:
         result = self.copy()
         result += other
         return result
 
-    def __radd__(self: TM, other: Union[str, Mapping, Iterable[Mapping]]) -> TM:
-        result = self.__class__(other)  # type: ignore
+    def __radd__(self: TM, other: Union[str, TMS, Iterable[TMS]]) -> TM:
+        result = self.__class__(other)
         return result + self
 
-    def __iadd__(self: TM, other: Union[str, Mapping, Iterable[Mapping]]) -> TM:
-        if isinstance(other, MessageSegment):
+    def __iadd__(self: TM, other: Union[str, TMS, Iterable[TMS]]) -> TM:
+        if isinstance(other, str):
+            self.extend(self._construct(other))
+        elif isinstance(other, MessageSegment):
             self.append(other)
-        elif isinstance(other, Message):
+        elif isinstance(other, Iterable):
             self.extend(other)
         else:
-            self.extend(self._construct(other))
+            raise ValueError(f"Unsupported type: {type(other)}")  # pragma: no cover
         return self
 
     @overload
     def __getitem__(self: TM, __args: str) -> TM:
-        ...
+        """
+        参数:
+            __args: 消息段类型
+
+        返回:
+            所有类型为 `__args` 的消息段
+        """
 
     @overload
     def __getitem__(self, __args: Tuple[str, int]) -> TMS:
-        ...
+        """
+        参数:
+            __args: 消息段类型和索引
+
+        返回:
+            类型为 `__args[0]` 的消息段第 `__args[1]` 个
+        """
 
     @overload
     def __getitem__(self: TM, __args: Tuple[str, slice]) -> TM:
-        ...
+        """
+        参数:
+            __args: 消息段类型和切片
+
+        返回:
+            类型为 `__args[0]` 的消息段切片 `__args[1]`
+        """
 
     @overload
     def __getitem__(self, __args: int) -> TMS:
-        ...
+        """
+        参数:
+            __args: 索引
+
+        返回:
+            第 `__args` 个消息段
+        """
 
     @overload
     def __getitem__(self: TM, __args: slice) -> TM:
-        ...
+        """
+        参数:
+            __args: 切片
+
+        返回:
+            消息切片 `__args`
+        """
 
     def __getitem__(
         self: TM,
@@ -231,25 +278,29 @@ class Message(List[TMS], abc.ABC):
         elif isinstance(arg1, str) and isinstance(arg2, slice):
             return self.__class__([seg for seg in self if seg.type == arg1][arg2])
         else:
-            raise ValueError("Incorrect arguments to slice")
+            raise ValueError("Incorrect arguments to slice")  # pragma: no cover
 
     def index(self, value: Union[TMS, str], *args) -> int:
         if isinstance(value, str):
-            first_segment = next((seg for seg in self if seg.type == value), None)  # type: ignore
-            return super().index(first_segment, *args)  # type: ignore
+            first_segment = next((seg for seg in self if seg.type == value), None)
+            if first_segment is None:
+                raise ValueError(f"Segment with type {value} is not in message")
+            return super().index(first_segment, *args)
         return super().index(value, *args)
 
     def get(self: TM, type_: str, count: Optional[int] = None) -> TM:
         if count is None:
             return self[type_]
 
-        iterator, filtered = (seg for seg in self if seg.type == type_), []
+        iterator, filtered = (
+            seg for seg in self if seg.type == type_
+        ), self.__class__()
         for _ in range(count):
             seg = next(iterator, None)
             if seg is None:
                 break
             filtered.append(seg)
-        return self.__class__(filtered)
+        return filtered
 
     def count(self, value: Union[TMS, str]) -> int:
         return len(self[value]) if isinstance(value, str) else super().count(value)
@@ -261,11 +312,11 @@ class Message(List[TMS], abc.ABC):
             obj: 要添加的消息段
         """
         if isinstance(obj, MessageSegment):
-            super(Message, self).append(obj)
+            super().append(obj)
         elif isinstance(obj, str):
             self.extend(self._construct(obj))
         else:
-            raise ValueError(f"Unexpected type: {type(obj)} {obj}")
+            raise ValueError(f"Unexpected type: {type(obj)} {obj}")  # pragma: no cover
         return self
 
     def extend(self: TM, obj: Union[TM, Iterable[TMS]]) -> TM:
@@ -281,10 +332,15 @@ class Message(List[TMS], abc.ABC):
     def copy(self: TM) -> TM:
         return deepcopy(self)
 
-    def extract_plain_text(self: "Message[MessageSegment]") -> str:
+    def extract_plain_text(self) -> str:
         """提取消息内纯文本消息"""
 
         return "".join(str(seg) for seg in self if seg.is_text())
 
 
-__autodoc__ = {"MessageSegment.__str__": True}
+__autodoc__ = {
+    "MessageSegment.__str__": True,
+    "MessageSegment.__add__": True,
+    "Message.__getitem__": True,
+    "Message._construct": True,
+}
diff --git a/tests/test_adapters/test_message.py b/tests/test_adapters/test_message.py
index 88d9e563..fd6bd5a4 100644
--- a/tests/test_adapters/test_message.py
+++ b/tests/test_adapters/test_message.py
@@ -1,23 +1,90 @@
+from pydantic import ValidationError, parse_obj_as
+
 from utils import make_fake_message
 
 
-def test_message_template():
-    from nonebot.adapters import MessageTemplate
-
+def test_segment_add():
     Message = make_fake_message()
+    MessageSegment = Message.get_segment_class()
 
-    template = MessageTemplate("{a:custom}{b:text}{c:image}", Message)
+    assert MessageSegment.text("text") + MessageSegment.text("text") == Message(
+        [MessageSegment.text("text"), MessageSegment.text("text")]
+    )
 
-    @template.add_format_spec
-    def custom(input: str) -> str:
-        return input + "-custom!"
+    assert MessageSegment.text("text") + "text" == Message(
+        [MessageSegment.text("text"), MessageSegment.text("text")]
+    )
 
-    formatted = template.format(a="test", b="test", c="https://example.com/test")
-    assert formatted.extract_plain_text() == "test-custom!test"
-    assert str(formatted) == "test-custom!test[fake:image]"
+    assert MessageSegment.text("text") + Message(
+        [MessageSegment.text("text")]
+    ) == Message([MessageSegment.text("text"), MessageSegment.text("text")])
+
+    assert "text" + MessageSegment.text("text") == Message(
+        [MessageSegment.text("text"), MessageSegment.text("text")]
+    )
 
 
-def test_message_slice():
+def test_segment_validate():
+    Message = make_fake_message()
+    MessageSegment = Message.get_segment_class()
+
+    assert parse_obj_as(
+        MessageSegment, {"type": "text", "data": {"text": "text"}}
+    ) == MessageSegment.text("text")
+
+    try:
+        parse_obj_as(MessageSegment, "some str")
+        assert False
+    except ValidationError:
+        assert True
+
+
+def test_segment():
+    Message = make_fake_message()
+    MessageSegment = Message.get_segment_class()
+
+    assert len(MessageSegment.text("text")) == 4
+    assert MessageSegment.text("text") != MessageSegment.text("other")
+    assert MessageSegment.text("text").get("data") == {"text": "text"}
+    assert list(MessageSegment.text("text").keys()) == ["type", "data"]
+    assert list(MessageSegment.text("text").values()) == ["text", {"text": "text"}]
+    assert list(MessageSegment.text("text").items()) == [
+        ("type", "text"),
+        ("data", {"text": "text"}),
+    ]
+
+    origin = MessageSegment.text("text")
+    copy = origin.copy()
+    assert origin is not copy
+    assert origin == copy
+
+
+def test_message_add():
+    Message = make_fake_message()
+    MessageSegment = Message.get_segment_class()
+
+    assert Message([MessageSegment.text("text")]) + MessageSegment.text(
+        "text"
+    ) == Message([MessageSegment.text("text"), MessageSegment.text("text")])
+
+    assert Message([MessageSegment.text("text")]) + "text" == Message(
+        [MessageSegment.text("text"), MessageSegment.text("text")]
+    )
+
+    assert Message([MessageSegment.text("text")]) + Message(
+        [MessageSegment.text("text")]
+    ) == Message([MessageSegment.text("text"), MessageSegment.text("text")])
+
+    assert "text" + Message([MessageSegment.text("text")]) == Message(
+        [MessageSegment.text("text"), MessageSegment.text("text")]
+    )
+
+    msg = Message([MessageSegment.text("text")])
+    msg += MessageSegment.text("text")
+    assert msg == Message([MessageSegment.text("text"), MessageSegment.text("text")])
+
+
+def test_message_getitem():
 
     Message = make_fake_message()
     MessageSegment = Message.get_segment_class()
@@ -52,3 +119,38 @@ def test_message_slice():
     assert message.get("image", 1) == Message([message["image", 0]])
 
     assert message.count("image") == 2
+
+
+def test_message_validate():
+    Message = make_fake_message()
+    MessageSegment = Message.get_segment_class()
+
+    Message_ = make_fake_message()
+
+    assert parse_obj_as(Message, Message([])) == Message([])
+
+    try:
+        parse_obj_as(Message, Message_([]))
+        assert False
+    except ValidationError:
+        assert True
+
+    assert parse_obj_as(Message, "text") == Message([MessageSegment.text("text")])
+
+    assert parse_obj_as(Message, {"type": "text", "data": {"text": "text"}}) == Message(
+        [MessageSegment.text("text")]
+    )
+
+    assert (
+        parse_obj_as(
+            Message,
+            [MessageSegment.text("text"), {"type": "text", "data": {"text": "text"}}],
+        )
+        == Message([MessageSegment.text("text"), MessageSegment.text("text")])
+    )
+
+    try:
+        parse_obj_as(Message, object())
+        assert False
+    except ValidationError:
+        assert True
diff --git a/tests/test_adapters/test_template.py b/tests/test_adapters/test_template.py
new file mode 100644
index 00000000..3dbef541
--- /dev/null
+++ b/tests/test_adapters/test_template.py
@@ -0,0 +1,17 @@
+from utils import make_fake_message
+
+
+def test_message_template():
+    from nonebot.adapters import MessageTemplate
+
+    Message = make_fake_message()
+
+    template = MessageTemplate("{a:custom}{b:text}{c:image}", Message)
+
+    @template.add_format_spec
+    def custom(input: str) -> str:
+        return input + "-custom!"
+
+    formatted = template.format(a="test", b="test", c="https://example.com/test")
+    assert formatted.extract_plain_text() == "test-custom!test"
+    assert str(formatted) == "test-custom!test[fake:image]"