A method is provided for accessing a legacy network, such as a 2G/3G network, through a temporary ID of an evolved network. User Equipment (UE) adds Mobility Management Entity (MME) information for uniquely identifying an MME accessed by the UE on an evolved network to an access message sent to an old network when the UE accesses the legacy network through a temporary ID of the evolved network. The legacy network selects a corresponding Serving GPRS Support Node (SGSN) for the UE according to the access message. After the MME information for uniquely identifying an MME is added to the access message sent to the old network, the legacy network can determine and find the MME that is accessed by the UE in the evolved network without changing a Radio Network Controller (RNC) and an SGSN on the legacy network.