Abstract: With the idea of ring signcryption, an efficient anonymous group key agreement scheme is presented based on the Bilinear Diffie-Hellman (BDH) assumption. The scheme establishes a secure group key under the premise of authenticating group members. For both internal and external group members the scheme achieves different degree of anonymity, that is, the external users can absolutely not learn any information about the internal membership structure, and the internal users only can find out the member composition but cannot recognize the identity of any member. In order to achieve the forward security and backward security of group key, new scheme supports group members to renew their group key when the external nodes join the group or the internal members leave the group. The proposed scheme can establish the group session key through only one round, and therefore, its computation complexity and storage cost are efficiently reduced.