The invention discloses a group call service processing method based on a cluster communication system. The method comprises the steps that: after establishing a group call, a core network device receives a group call downlink data packet from a data source; and the core network device sends the group call downlink data packet to a bearer network, wherein a multicast distribution tree is preset in the bearer network, and the multicast distribution tree employs the core network device as a multicast source and employs a participant base station in a multicast group as a leaf node. In the method, the core network device only needs to send a copy of data to realize the point-to-multipoint multicast transmission mode from the core network device to a group call terminal, thereby reducing the load of the core network device and the redundant flow of the bearer network, reducing the transmission delay and improving the capacity and the performance of the cluster service on the whole.