A method for realizing ring back tone in communication system, enabling that the calling user can only hear the ring back tone triggered by the primary called user no matter whether the call is forwarded or how it is forwarded. In the present invention, service control unit sets a mark indicating not to request ring resource in Invite message initiated to the forward user, and indicating the backward service control unit not to request triggering the ring resource. Optionally, service control unit only sends ringing message forwardly when it receives the backward ringing message and succeeds to request ring resource, and when it receives the backward ringing message, if service control unit has ever initiated call forward, then it deactivates backward ring resource. Optionally, each service control unit requests ring resource respectively, and forwards it when it receives 200 OK, where a mark indicating it coming from ring resource is set; service control unit deactivates backward ring resource, if it finds the mark in the backward 200 OK.