A method, system, and device for converting session control signaling are provided. The method includes at least one of the following steps: a first adaptation unit converts a session control signaling message of a circuit switched (CS) session leg into a session control signaling message of an IP multimedia subsystem (IMS) session leg; or the first adaptation unit converts a session control signaling message of an IMS session leg into a session control signaling message of a CS session leg. In embodiments of the present invention, an adaptation unit intercepts a CS signaling message after an inter-mobile switching center (MSC) handover, and converts CS signaling messages to IMS signaling messages and vice versa, so that the IMS domain may continue to control a session after the inter-MSC handover.