With the rapid development of wireless mesh networks (WMNs) technology, more and more commercial products and even solutions are provided in trial applications. Especially, the 802.11-based WMNs are considered as one of the best networking technology to extend the coverage of wireless LAN. However, few practical optimization tools are available for the planning and design of commercial WMNs. In this paper, the channel assignment tool (CAT) designed for the optimized backhaul networking of multi-radio multi-channel (MRMC) WMNs is presented. In the proposed channel assignment algorithm, several crucial factors affecting real networking performance are taken into account. Besides, the CAT is implemented as a flexible software module, which can be easily combined with other optimization and planning tool, as well as works independently. Furthermore, through the outdoor test taken on the test-bed consisting of commercial wireless mesh routers, the optimal channel assignment scheme figured out by the CAT is verified to perform best in the real MRMC WMN.