a method for implementing unified authentication for user logon , the method comprising the steps of : establishing an authentication server ; creating a user authentication account number in the authentication server ; storing user information which the user uses in a plurality of systems into the authentication server ; associating , in the authentication server , the created user authentication account number with the user information which the user uses in the plurality of systems ; and providing an authentication flag to the client of the user by the authentication server based on the association between the user authentication account number and the user information which the user uses in the plurality of systems established in the authentication server so that the user can log on the plurality of systems using the authentication flag . the present invention is applied to provide a unified mechanism of user logon authentication in integration and mergence of the service processes provided by a plurality of internet information systems or internet providers , and thus the user can access all authorized application systems or service providers with only one logon authentication .