A method of interface communication between entities in soft switch system in NGN, and a method and apparatus for Gateway Control Protocol (GCP) message transmission are disclosed, so that H.248 messages can be transmitted between Media Gateway Controller and Media Gateway over MTP3B/ATM, hence full advantages of resources are taken in existing optical fiber networks and E1/T1 networks, so as to improve the networking flexibility and reduce the cost. The internal data transmission mechanism between MTP3B protocol layer and H.248 protocol layer is established via an M3H adaptation layer; load sharing between H.248 processing modules is enabled by establishing mapping between H.248 links and MTP3B signaling points; the adaptation relationship between MTP3B layer and H.248 layer is implemented by configuring and maintaining logic relationship between table of LinkSets, H.248-MTP3B mapping table, and table of H.248 processing modules, thus implementing the mechanism of bearing H.248 messages over MTP3B.