diff --git a/backend/app/admin/crud/crud_user.py b/backend/app/admin/crud/crud_user.py
index 8f79df54..d6155ce9 100644
--- a/backend/app/admin/crud/crud_user.py
+++ b/backend/app/admin/crud/crud_user.py
@@ -87,7 +87,6 @@ class CRUDUser(CRUDPlus[User]):
         :param obj: 注册用户参数
         :return:
         """
-        obj.avatar = str(obj.avatar)  # noqa: fix pgsql compatibility
         dict_obj = obj.model_dump()
         dict_obj.update({'is_staff': True, 'salt': None})
         new_user = self.model(**dict_obj)
@@ -110,7 +109,6 @@ class CRUDUser(CRUDPlus[User]):
         role_ids = obj.roles
         del obj.roles
 
-        obj.avatar = str(obj.avatar)  # noqa: fix pgsql compatibility
         count = await self.update_model(db, input_user.id, obj)
 
         stmt = select(Role).where(Role.id.in_(role_ids))
diff --git a/backend/app/admin/schema/user.py b/backend/app/admin/schema/user.py
index 32c8b643..c17a8753 100644
--- a/backend/app/admin/schema/user.py
+++ b/backend/app/admin/schema/user.py
@@ -1,13 +1,13 @@
 from datetime import datetime
-from typing import Any
+from typing import Annotated, Any
 
-from pydantic import ConfigDict, Field, HttpUrl, model_validator
+from pydantic import ConfigDict, Field, HttpUrl, PlainSerializer, model_validator
 from typing_extensions import Self
 
 from backend.app.admin.schema.dept import GetDeptDetail
 from backend.app.admin.schema.role import GetRoleWithRelationDetail
 from backend.common.enums import StatusType
-from backend.common.schema import CustomEmailStr, CustomPhoneNumber, SchemaBase
+from backend.common.schema import CustomEmailStr, CustomPhoneNumber, SchemaBase, ser_string
 
 
 class AuthSchemaBase(SchemaBase):
@@ -40,7 +40,7 @@ class AddOAuth2UserParam(AuthSchemaBase):
     password: str | None = Field(None, description='密码')
     nickname: str | None = Field(None, description='昵称')
     email: CustomEmailStr | None = Field(None, description='邮箱')
-    avatar: HttpUrl | None = Field(None, description='头像地址')
+    avatar: Annotated[HttpUrl, PlainSerializer(ser_string)] | None = Field(None, description='头像地址')
 
 
 class ResetPasswordParam(SchemaBase):
@@ -57,7 +57,7 @@ class UserInfoSchemaBase(SchemaBase):
     dept_id: int | None = Field(None, description='部门 ID')
     username: str = Field(description='用户名')
     nickname: str = Field(description='昵称')
-    avatar: HttpUrl | None = Field(None, description='头像地址')
+    avatar: Annotated[HttpUrl, PlainSerializer(ser_string)] | None = Field(None, description='头像地址')
     email: CustomEmailStr | None = Field(None, description='邮箱')
     phone: CustomPhoneNumber | None = Field(None, description='手机号')
 
diff --git a/backend/common/schema.py b/backend/common/schema.py
index 6eae4aa7..e3b29810 100644
--- a/backend/common/schema.py
+++ b/backend/common/schema.py
@@ -1,5 +1,5 @@
 from datetime import datetime
-from typing import Annotated
+from typing import Annotated, Any
 
 from pydantic import BaseModel, ConfigDict, EmailStr, Field, validate_email
 
@@ -27,3 +27,9 @@ class SchemaBase(BaseModel):
             else timezone.to_str(x),
         },
     )
+
+
+def ser_string(value: Any) -> str | None:
+    if value:
+        return str(value)
+    return value