diff --git a/app/Login.py b/app/Login.py
index f1317b2..64612bc 100644
--- a/app/Login.py
+++ b/app/Login.py
@@ -1,4 +1,5 @@
 import hashlib
+import string
 from datetime import datetime
 from UseSqlite import InsertQuery, RecordQuery
 
@@ -81,3 +82,35 @@ def md5(s):
     '''
     h = hashlib.md5(s.encode(encoding='utf-8'))
     return h.hexdigest()
+
+
+class UserName:
+    def __init__(self, username):
+        self.username = username
+
+    def validate(self):
+        if len(self.username) > 20:
+            return f'{self.username} is too long.  The user name cannot exceed 20 characters.'
+        if self.username.startswith('.'): # a user name must not start with a dot
+            return 'Period (.) is not allowed as the first letter in the user name.'
+        if ' ' in self.username: # a user name must not include a whitespace
+            return 'Whitespace is not allowed in the user name.'
+        for c in self.username: # a user name must not include special characters, except non-leading periods or underscores
+            if c in string.punctuation and c is not '.' and c is not '_':
+                return f'{c} is not allowed in the user name.'
+        return 'OK'
+
+
+class WarningMessage:
+    def __init__(self, s):
+        self.s = s
+
+    def __str__(self):
+        result = UserName(self.s).validate()
+        if result != 'OK':
+            return result
+
+        if self.s in ['signup', 'login', 'logout', 'reset', 'mark', 'back', 'unfamiliar', 'familiar', 'del']:
+            return 'You used a restricted word as the user name.  Please come up with a better one.'
+
+        return 'OK'
diff --git a/app/account_service.py b/app/account_service.py
index 0e5cf7a..4aafe67 100644
--- a/app/account_service.py
+++ b/app/account_service.py
@@ -1,6 +1,5 @@
 from flask import *
-from Login import check_username_availability, verify_user, add_user, get_expiry_date, change_password
-import re
+from Login import check_username_availability, verify_user, add_user, get_expiry_date, change_password, UserName, WarningMessage
 
 # 初始化蓝图
 accountService = Blueprint("accountService", __name__)
@@ -22,17 +21,9 @@ def signup():
         password = escape(request.form['password'])
         
         #! 添加如下代码为了过滤注册时的非法字符
-        if len(username) > 20:
-            return '用户名过长'
-        # 正则匹配非法字符
-        check_useful = re.search(u'^[_a-zA-Z0-9\u4e00-\u9fa5]+$', username)
-        if not check_useful:
-            return '存在非法字符'
-        # 判断用户名是否和接口重名
-        if username in ["signup", "login", "logout", 
-                        "reset", "mark", "back", 
-                        "unfamiliar", "familiar", 'del']:
-            return '请勿与接口同名'
+        warn = WarningMessage(username)
+        if str(warn) != 'OK':
+            return str(warn)
         
         available = check_username_availability(username)
         if not available: # 用户名不可用
@@ -140,4 +131,4 @@ alert('密码修改失败');
 window.location.href="/reset";
 </script>
 
-'''
\ No newline at end of file
+'''