Group key agreement problem is important in many modern collaborative and distributed applications. In this paper, based on bilinear pairings cryptosystem, an efficient constant-round keys agreement is proposed for multi-party?s communication, which can not only establish a group key for all participators but also establish key for every party that is a group too. Compared with other constant-round contributory key agreement, it is no need for about half of group members to broadcast messages in second round information exchange, so it saves communication cost largely.