A method and system for automatically logging in a client is disclosed in the present invention, mainly comprising: use encrypted ICCID for the authentification of user's identity during automatic login; when authentification is passed, determine the account information corresponding to the identification of the client to be logged in currently by the user, and log in the client automatically with the determined account information, so that the user can conveniently manage the account information corresponding to each client when he guarantees the security of the account information simultaneously, avoiding the troublesome inputting of username and password of the account and achieving the purpose of automatically logging in a client.