The present invention discloses a method for implementing simulation services, including the following: an interworking control unit obtains the CS domain network user identifier after detecting that the call signaling message from the CS domain network carries no CS domain network user identifier, puts the obtained user identifier into the SIP message, which is subsequently sent to the IMS network; the IMS network processes the PSTN/ISDN simulation services according to the user identifier. The present invention also discloses a system for implementing simulation service. The present invention makes it unnecessary to extend the existing SIP protocol and to perform signaling interaction between the IMS network and the interworking control unit for obtaining the user identifier, thus simplifying the implementation of the PSTN/ISDN simulation services.