In this paper, the traffic confidentiality and study of the traffic pattern concealment problem via routing control is focused. First, the number of nodes in a WMN is limited. Second, traffic forwarding relationship among nodes is strongly dependent on their locations and the network topology, which is static and known a priori in WMN. To better utilize the wireless channel resource and enhance the data delivery performance, a short path is usually selected. In light of these problems, it is aimed to design a light weight traffic privacy preserving mechanism for WMN. The penalty-based routing algorithm is proposed to achieve the goal of hiding traffic pattern by exploiting the richness of available paths between two nodes in WMN. The algorithm operates in three phases, path pool generation, candidate path selection and individual packet routing. These results show that with this algorithm, the destination node is able to consistently limit the proportion of mutual information it shares with the observing nodes