The real-time message transmitting method is used in multimedia communication system to transmit real-time message in signaling channel. The signaling message is expanded correspondingly and the real-time message is transmitted via the expanded signaling message simply. For multipoint service, the real-time message is transmitted via MCU or other transfer equipment in relatively low cost. Furthermore, the real-time message is well fused with video and audio service and may be superposed onto video image for output conveniently without using alone data meeting server. The real-time message maybe transmitted via H.245 control channel, etc., with the H.245 protocol being part of the H.323 protocol application. By means of solving the NAT problem and fire wall problem of H.323 protocol application, the problem of bi-directional penetration of real-time message in NAT equipment may be solved.