Recently, the CR (cognitive radio) technology is gathering more and more attention because it has the capacity to deal with the scarce of the precious spectrum resource. Within the domain of CR technology, channel management of CR is of utmost importance due to its key role in the performance enhancement of the transmission. A group-based DCA (dynamic channel allocation) MAC protocol in CR network has been proposed in this paper. It divides the channels into several groups which consist of the data channels and common control channel. We analyze the throughput under saturation condition, and the simulation results show that by using our protocol the throughput is improved obviously compared with traditional DCA.