In this paper we have considered the channel assignment problem in multi-channel multi-radio wireless mesh networks. The problem is to assign channels to links in the network with the original topology preservation, and aim at minimizing the overall network interference which is proved to be NP-hard. We have first illustrated that the conversion from the channel assignment problem to the max k-cut or min k-partition problem cannot correctly evaluate the network interference because of the broadcasting characteristic of the wireless communication in wireless networks. In this paper we have developed a centralized heuristic algorithm for the channel assignment due to the NP-hardness of the problem. Extensive simulation results have demonstrated that our algorithm has good performance in both dense and sparse networks compared with related works. The theoretic and experiment results have shown that the proposed algorithms serve as a practical solution to the channel assignment problem in the multi-channel multi-radio wireless mesh networks.