The invention provides a cluster group call service encryption method and a cluster core network. The cluster group call service encryption method comprises the following steps: the cluster core network adjusts a preset first group call parameter after completing the calling of each group call, wherein the first group call parameter is used to indicate the call times of the group call; the clustercore network obtains a new key with a preset key deduction algorithm according to the root key information and the first group call parameter; and the cluster core network sends the first group callparameter to the cluster terminal corresponding to the group in the group call process, so that the cluster terminal confirms the new key according to the first group call parameter and the root key information obtained in advance. The invention reaches the request of one call to one key in the cluster group call process with high security and less changes to the standard.