A method and system for transferring user equipment (UE) in a mobile communication system are provided. According to the method, a source core (CN) network determines to transfer a UE that it serves and sends a transfer instruction carrying UE transfer restriction information to the UE; an access network receives a transfer request that is sent by the UE according to the restriction information carried in the transfer instruction; the access network selects a target CN entity that is different from the source CN entity for the UE; and the UE is transferred to the target CN entity. The method and system provided by the disclosure are applicable to user transferring between CN entities in any communication network. The transferring is initiated by a network side entity, and a more preferable CN entity is selected for the UE to provide a better service.