Secure group communication is becoming more and more important in internet. In order to provide a secure and reliable communication among the members of a conference over a public network, all group members must have the ability to establish a common secret key. We call this kind of the public key distribution system is a conference key distribution system (CKDS). Our protocol bases on the two-party Diffie-Hellman protocol to build intermediate keys from each subgroups gradually until the entire conference key is obtained. The process of forming the entire conference key will constructed a ripple structure which reduce the times of encryption and decryption than butterfly scheme key distribution systems. Our protocol promote the efficiency of a conference key distribution system.