System selection method for interlocking networks of mobile communication system

PURPOSE: A system selection method for interlocking networks of a mobile communication system is provided to utilize idle installation of an existing network positively by providing a system selection function between a new network and an existing network. CONSTITUTION: An MS(Mobile Station) registers a position to an MSC(Mobile Switching Station)/VLR(Visitor Location Register) of a new serving system(201). A position registration of the MSC/VLR of an old serving system is cancelled via a HLR(Home Location Register) and a position registration including a subscriber's profile is performed to the MSC/VLR of the new serving system(202-205). By discriminating existence of a service redirection to a preferred serving system, if there is redirection, a service redirection message is transmitted to the MS(206). The MS registers a position to an MSC/VLR of a preferred serving system(207). A position registration of the MSC/VLR of a new serving system is cancelled via an HLR(Home Location Register) and a position registration including a subscriber's profile is performed in the MSC/VLR of the preferred serving system(208-210).