diff --git a/app/account_service.py b/app/account_service.py
index a7ed0c4..e4ff95b 100644
--- a/app/account_service.py
+++ b/app/account_service.py
@@ -23,11 +23,39 @@ def signup():
         #! 添加如下代码为了过滤注册时的非法字符
         warn = WarningMessage(username)
         if str(warn) != 'OK':
-            return jsonify({'status': '3', 'warn': str(warn)})
+            return str(warn)
+            # return jsonify({'status': '3', 'warn': str(warn)})
         
         available = check_username_availability(username)
         if not available: # 用户名不可用
-            return jsonify({'status': '0'})
+            flash('用户名 %s 已经被注册。' %(username))
+            return render_template('signup.html')
+        elif len(password.strip()) < 8: # 密码过短
+            return '密码少于8位。'
+            # return jsonify({'status': '0'})
+
+        has_specialchar = False
+        specialchar_list = ['+', '-', '*', '/', '_', '&', '%', ',']
+        for c in password.strip():
+            if c in specialchar_list:
+                has_specialchar = True
+                break
+        if not has_specialchar:
+            return '密码必须包含特殊字符'
+
+        has_upper_letter = False
+        has_lower_letter = False
+        for c in password.strip():
+            if c.isupper():
+                has_upper_letter = True
+            elif c.islower():
+                has_lower_letter = True
+            has_both_letter = has_upper_letter and has_lower_letter
+            if has_both_letter:
+                break
+        if not has_both_letter:
+            return '密码必须同时包含大写字母和小写字母'
+
         else: # 添加账户信息
             add_user(username, password)
             verified = verify_user(username, password)