diff --git a/api/apps/user_app_fastapi.py b/api/apps/user_app_fastapi.py
index 0cefc5c..9fa3f9e 100644
--- a/api/apps/user_app_fastapi.py
+++ b/api/apps/user_app_fastapi.py
@@ -443,8 +443,9 @@ async def user_add(request: RegisterRequest):
             detail=f"Invalid email address: {email_address}!"
         )
 
-    # 检查邮箱地址是否已被使用
-    if UserService.query(email=email_address):
+    # 检查邮箱地址是否已被使用（大小写不敏感）
+    existing_users = UserService.query_user_by_email_insensitive(email_address)
+    if existing_users:
         raise HTTPException(
             status_code=status.HTTP_400_BAD_REQUEST,
             detail=f"Email: {email_address} has already registered!"