The method includes steps: (1) source SGSN for MS to be migrated to redistribute P-TMSI including target NRI and ID in non - broadcasting route domain, which are sent to MS; (2) MS sends initial NAS message carried with redistributed P-TMSI and ID in non - broadcasting route domain to RAN; RAN forwards the message to target SGSN corresponding to target NRI included in P-TMSI; (3) after receiving initial NAS message carrying ID in non - broadcasting route domain, target SGSN carries out route domain update process for MS. in addition, the invention also discloses a system for implementing load migration in pool range and a SGSN. The invention raises flexibility for migrating loads in pool, and raises satisfying degree of operation manager. |