diff --git a/app/Login.py b/app/Login.py
index db4df18..cd750d1 100644
--- a/app/Login.py
+++ b/app/Login.py
@@ -3,6 +3,18 @@ import string
 from datetime import datetime, timedelta
 from UseSqlite import InsertQuery, RecordQuery
 
+def md5(s):
+    '''
+    MD5摘要
+    :param str: 字符串
+    :return: 经MD5以后的字符串
+    '''
+    h = hashlib.md5(s.encode(encoding='utf-8'))
+    return h.hexdigest()
+
+# import model.user after the defination of md5(s) to avoid circular import
+from model.user import get_user_by_username, insert_user, update_password_by_username
+
 path_prefix = '/var/www/wordfreq/wordfreq/'
 path_prefix = './'  # comment this line in deployment
 
@@ -12,13 +24,9 @@ def verify_pass(newpass,oldpass):
 
 
 def verify_user(username, password):
-    rq = RecordQuery(path_prefix + 'static/wordfreqapp.db')
-    password = md5(username + password)
-    rq.instructions_with_parameters("SELECT * FROM user WHERE name=:username AND password=:password", dict(
-        username=username, password=password))  # the named style https://docs.python.org/3/library/sqlite3.html
-    rq.do_with_parameters()
-    result = rq.get_results()
-    return result != []
+    user = get_user_by_username(username)
+    encoded_password = md5(username + password)
+    return user is not None and user.password == encoded_password
 
 
 def add_user(username, password):
@@ -26,19 +34,12 @@ def add_user(username, password):
     expiry_date = (datetime.now() + timedelta(days=30)).strftime('%Y%m%d') # will expire after 30 days
     # 将用户名和密码一起加密，以免暴露不同用户的相同密码
     password = md5(username + password)
-    rq = InsertQuery(path_prefix + 'static/wordfreqapp.db')
-    rq.instructions_with_parameters("INSERT INTO user VALUES (:username, :password, :start_date, :expiry_date)", dict(
-        username=username, password=password, start_date=start_date, expiry_date=expiry_date))
-    rq.do_with_parameters()
+    insert_user(username=username, password=password, start_date=start_date, expiry_date=expiry_date)
 
 
 def check_username_availability(username):
-    rq = RecordQuery(path_prefix + 'static/wordfreqapp.db')
-    rq.instructions_with_parameters(
-        "SELECT * FROM user WHERE name=:username", dict(username=username))
-    rq.do_with_parameters()
-    result = rq.get_results()
-    return result == []
+    existed_user = get_user_by_username(username)
+    return existed_user is None
 
 
 def change_password(username, old_password, new_password):
@@ -54,35 +55,16 @@ def change_password(username, old_password, new_password):
     # 将用户名和密码一起加密，以免暴露不同用户的相同密码
     if verify_pass(new_password,old_password): #新旧密码一致
         return False
-    password = md5(username + new_password)
-    rq = InsertQuery(path_prefix + 'static/wordfreqapp.db')
-    rq.instructions_with_parameters("UPDATE user SET password=:password WHERE name=:username", dict(
-        password=password, username=username))
-    rq.do_with_parameters()
+    update_password_by_username(username, new_password)
     return True
 
 
 def get_expiry_date(username):
-    rq = RecordQuery(path_prefix + 'static/wordfreqapp.db')
-    rq.instructions_with_parameters(
-        "SELECT expiry_date FROM user WHERE name=:username", dict(username=username))
-    rq.do_with_parameters()
-    result = rq.get_results()
-    if len(result) > 0:
-        return result[0]['expiry_date']
-    else:
+    user = get_user_by_username(username)
+    if user is None:
         return '20191024'
-
-
-def md5(s):
-    '''
-    MD5摘要
-    :param str: 字符串
-    :return: 经MD5以后的字符串
-    '''
-    h = hashlib.md5(s.encode(encoding='utf-8'))
-    return h.hexdigest()
-
+    else:
+        return user.expiry_date
 
 class UserName:
     def __init__(self, username):
diff --git a/app/model/user.py b/app/model/user.py
index 28173b9..d684332 100644
--- a/app/model/user.py
+++ b/app/model/user.py
@@ -1,5 +1,6 @@
 from model import *
 from Login import md5
+from pony import orm
 
 def get_users():
     with db_session:
@@ -11,6 +12,11 @@ def get_user_by_username(username):
         if user:
             return user.first()
 
+def insert_user(username, password, start_date, expiry_date):
+    with db_session:
+        user = User(name=username, password=password, start_date=start_date, expiry_date=expiry_date)
+        orm.commit()
+
 def update_password_by_username(username, password="123456"):
     with db_session:
         user = User.select(name=username)