Method and system for keeping consistency of user identifications of terminal in different networks

The invention discloses a method and a system for keeping consistency of user identifications of a terminal in different networks, wherein the method comprises the steps of: presetting an internet protocol (IP) mapping relation chart by an authentication server of a core network; sending an identification request message to a terminal by the authentication server; receiving an identification response message of the terminal by the authentication server; analyzing the identification response message by the authentication server, and acquiring the international mobile subscriber identity (IMSI) or user name of the terminal; depending on the IMSI or the user name, finding an IP address which corresponds to the IMSI or the user name in the IP mapping relation chart which is preset by the authentication server; and sending the IP address which corresponds to the IMSI or the user name to the terminal by the authentication server. With addition of an IP mapping relation chart in the authentication equipment of the c