In order to avoid security threats caused by password attack and replay attack in single sign-on protocal, the most methods on sovling these issues are making use of complicated techniques and equipment, no-doubt this increases the degree of complication and cost of the system, and reduces the usability as well. In this regard, this study proposes an new scheme based on dynamic double password and log feedback, the two passwords are used in user's login and application of service, and the user can be able to make a judgement on security of a password throuth auditting the log file and allowed to modify the password, the result analysis indicates that new scheme greatly enhances the capability of guarding against password attack of the system. Meanwhile, as the new increaed data flow in new scheme is directly going to relevant server without passing client, the security gravity of the client is reduced, and also it is benefit to protecting against replay attack; furthermore, the us...