In the architecture of wireless sensor network, routing technology at the network layer is essential. Since the clustering routing leads in good performance on data aggregation, energy minimization and so on, it has become the focus of the study routing. In this paper, a cluster-based routing tree construction algorithm for Wireless Sensor Networks is proposed. The detail of how to select the intermediate nodes to build the routing gathering tree is also described. The experiments show that the algorithm is effective to extend the network lifetime.