Registration method, sgsn and user equipment

Embodiments of the present invention relate to a registration method, an SGSN and a user equipment. The registration method comprises: after receiving a periodic routing area update (RAU) request message sent by a user equipment (UE), a second general packet radio service technology service support node (SGSN) determines, according to routing area identity (RAI) information carried by the periodic RAU request message, that the UE has migrated from a first SGSN to the second SGSN, the UE having co-registered in the first SGSN, and the first SGSN and the second SGSN belonging to the same SGSN pool; the second SGSN notifies the UE to perform co-registration. The embodiments of the invention, by enabling the UE to maintain joint registration in the SGSN pool, ensure that circuit switched domain (CS) voice services of the migrated UE are smoother, thereby improving user experience of CS voice services.