diff --git a/nonebot/adapters/_template.py b/nonebot/adapters/_template.py
index fad17d84..82903dc5 100644
--- a/nonebot/adapters/_template.py
+++ b/nonebot/adapters/_template.py
@@ -4,6 +4,9 @@ from string import Formatter
 from typing import (
     TYPE_CHECKING,
     Any,
+    Callable,
+    Dict,
+    Optional,
     Set,
     List,
     Type,
@@ -23,6 +26,9 @@ if TYPE_CHECKING:
 TM = TypeVar("TM", bound="Message")
 TF = TypeVar("TF", str, "Message")
 
+FormatSpecFunc = Callable[[Any], str]
+FormatSpecFunc_T = TypeVar("FormatSpecFunc_T", bound=FormatSpecFunc)
+
 
 class MessageTemplate(Formatter, Generic[TF]):
     """消息模板格式化实现类"""
@@ -50,8 +56,18 @@ class MessageTemplate(Formatter, Generic[TF]):
           * ``template: Union[str, Message]``: 模板
           * ``factory: Union[str, Message]``: 消息构造类型，默认为 `str`
         """
-        self.template: Union[str, TF] = template
+        self.template: TF = template
         self.factory: Type[TF] = factory
+        self.format_specs: Dict[str, FormatSpecFunc] = {}
+
+    def add_format_spec(
+        self, spec: FormatSpecFunc_T, name: Optional[str] = None
+    ) -> FormatSpecFunc_T:
+        name = name or spec.__name__
+        if name in self.format_specs:
+            raise ValueError(f"Format spec {name} already exists!")
+        self.format_specs[name] = spec
+        return spec
 
     def format(self, *args: Any, **kwargs: Any) -> TF:
         """
@@ -69,7 +85,7 @@ class MessageTemplate(Formatter, Generic[TF]):
         else:
             raise TypeError("template must be a string or instance of Message!")
 
-        return msg
+        return msg  # type:ignore
 
     def vformat(
         self, format_string: str, args: Sequence[Any], kwargs: Mapping[str, Any]
@@ -155,25 +171,16 @@ class MessageTemplate(Formatter, Generic[TF]):
         )
 
     def format_field(self, value: Any, format_spec: str) -> Any:
-        if issubclass(self.factory, str):
-            return super().format_field(value, format_spec)
-
-        segment_class: Type[MessageSegment] = self.factory.get_segment_class()
-        method = getattr(segment_class, format_spec, None)
-        method_type = inspect.getattr_static(segment_class, format_spec, None)
+        formatter: Optional[FormatSpecFunc] = self.format_specs.get(format_spec)
+        if (formatter is None) and (not issubclass(self.factory, str)):
+            segment_class: Type["MessageSegment"] = self.factory.get_segment_class()
+            method = getattr(segment_class, format_spec, None)
+            if inspect.ismethod(method):
+                formatter = getattr(segment_class, format_spec)
         return (
-            (
-                super().format_field(value, format_spec)
-                if (
-                    (method is None)
-                    or (
-                        not isinstance(method_type, (classmethod, staticmethod))
-                    )  # Only Call staticmethod or classmethod
-                )
-                else method(value)
-            )
-            if format_spec
-            else value
+            super().format_field(value, format_spec)
+            if formatter is None
+            else formatter(value)
         )
 
     def _add(self, a: Any, b: Any) -> Any:
diff --git a/tests/adapters/test_template.py b/tests/adapters/test_template.py
new file mode 100644
index 00000000..3dbef541
--- /dev/null
+++ b/tests/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]"
diff --git a/tests/utils.py b/tests/utils.py
index d516665f..a8d0c0ed 100644
--- a/tests/utils.py
+++ b/tests/utils.py
@@ -18,14 +18,18 @@ def make_fake_message() -> Type["Message"]:
             return FakeMessage
 
         def __str__(self) -> str:
-            return self.data["text"]
+            return self.data["text"] if self.type == "text" else f"[fake:{self.type}]"
 
         @classmethod
         def text(cls, text: str):
             return cls("text", {"text": text})
 
+        @classmethod
+        def image(cls, url: str):
+            return cls("image", {"url": url})
+
         def is_text(self) -> bool:
-            return True
+            return self.type == "text"
 
     class FakeMessage(Message):
         @classmethod