The invention discloses a user switch-in control method and system of IMS realm, which comprises the following steps: proceeding sectionalization management for user according to IMPU and attribute at HSS; making the user in the same group possess the same switch-in ability; adopting the same S-CSCF to proceed dynamic switch-in control for the same group user; modifying user register flow path and HSS/S-CSCF interface to make the same group user obtain the same S-CSCF service; downloading relative information of user as well as user register information simultaneously through S-CSCF; managing user switch-in control through S-CSCF according to strategy dynamic sectionalization; realizing dynamic network calling control.