Method and system for service registration at ip multimedia subsystem

PURPOSE: A method and a system for registering a service in an IP multimedia sub system are provided to actively register the third service through a registration proxy server without generating an initial filter reference for the third party services which are not saved in a user profile. CONSTITUTION: A terminal(170) generates a registration request message including the third party application server address list. The terminal transmits the registration request message by an S-CSCF(Serving Call Session Control Function)(130). The S-CSCF compares the registration request message with iFC(Initial Filter Criteria) of an HSS(Home Subscriber Server)(140). A registration proxy server extracts the third party application server address list by parsing of the registration request message of the S-CSCF. The registration proxy server transmits the registration request message to the third party application server(160).