The invention discloses a method for realizing service interaction of an IP multimedia subsystem (IMS), which is simple and practicable. Each service logic component has a unique service identifier. The method comprises the following steps: (a) a serving-call session control function (S-CSCF) sends a session initiation protocol (SIP) request message to an application server (AS) or a service capability interaction manager (SCIM) of a user request service; (b) the AS or the SCIM receives the SIP request, performs the service, inserts the service identifier of the service into the SIP request, and returns the SIP request carrying the service identifier back to the S-CSCF.