The present invention relates to a method, a system and a device for implementing interconnection between IP domains. The method mainly includes: first, the Media Gateway Controller (MGC) sends the IP domain information of the IP domain to which the media stream to be created pertains to the Media Gateway (MG) between IP domains; when the MG receives the IP domain information for creating the media stream from the MGC, the MG creates the corresponding media stream between the IP domains according to the IP domain information, thus implementing the interconnection between the IP domains.