In Wireless Mesh Networks(WMNs) for Internet access, service quality of different users will vary greatly depending on the locations of users. In this study, WMNs were simulated as queuing networks and the delay variance of different users in unsaturated load case were analyzed. The analytical results indicated that delay fairness could be guaranteed by setting multiple buffers in mid-node and scheduling priorities of all flows. The priority assignment problem was formulated as a combinatorial optimization problem which was targeted to achieve maximal fairness, and a solution was also provided. The fairness was evaluated by using Lorenz curve. Simulation results show that better fairness index can be acquired by using optimal assignment algorithm.