The present invention relates to a method and a system for authentication processing, a 3rd Generation Partnership Project (3GPP) Authentication, and Authorization Accounting (AAA) server, and a User Equipment (UE). The method includes: receiving an authentication request message that carries authentication mode indication information; determining an authentication mode according to the authentication mode indication information; and performing authentication processing according to the authentication mode. The system for authentication processing includes the 3GPP AAA server and a network device which enables the UE to access the 3GPP AAA server through the network device. Through the method and the system for authentication processing, the 3GPP AAA server and the UE provided herein, the authentication request message sent by the UE carries the authentication mode indication information which has different parameter values so that the 3GPP AAA server can distinguish different authentication modes and perform the authentication processing according to the determined authentication mode.