Wireless mesh networks (WMNs) are emerging as a favorable technology for last-mile Internet access. Nodes in WMNs can be equipped with multiple interfaces which work in different channels to increase the available bandwidth. However, efficient channel assignment schemes are still needed due to the interference effect and the limited number of orthogonal channels. In this paper, we consider the channel assignment and routing for dynamic traffic in WMNs. We adopt the static channel assignment strategy to the network interfaces. The problem is simplified into two sequential stages. The first is to assign channels to interfaces while the second is to determine the route for each coming traffic demand. We propose a Mixed Integer Linear Programming (MILP) formulation to the problem and develop a simulated annealing based channel assignment algorithm for the channel assignment. The shortest path routing is adopted for the dynamic traffic. Simulation results show the network throughput and blocking probability under different network scenarios.