Abstract: A multicast rekeying protocol is analyzed based on hierarchical K-ary tree （HKT） and a multicast rekeying protocol based on OKCT is proposed when a member joins and leaves the communication group. The protocol's performance is analyzed. The protocol keeps the group controller and members' key space, and decreases the number of rekeying messages when a member joins and leaves the communication group into log_k n and （k-1）log_k n-1, and decreases the quantity of computation when the group controller encrypts the rekeying message and the members decrypt the rekeying message.