Abstract: The present invention provides a method for providing message transmission in H.323 communication system. The method includes: the first endpoint and second endpoint confirming authentication information through a GK; according to said authentication information, the first endpoint and second endpoint exchanging message directly. Since H.235 protocol of ITU-T describes the authentication and privacy technique used in H.323 systems and provides security service for message transmission in GK-routed model, the present invention can guarantee the security of the authentication information. The functions of middle entities need not to be modified for applying the method provided by the present invention because Diffie-Hellman key exchange technology is adopted in this method. The present invention increases the network scalability of the symmetric key system by adopting negotiation mode. The present invention designates and improves the security framework of message transmission in direct-routed model of H.