Abstract: In the paper we formulate the WSNs with a two-tier architecture, where the cluster head nodes partitioned into the upper tier are studied, and the routing problem is analyzed with the time-varying data rate, then a time-varying bit rate routing algorithm based on data fusion(TBRRDF) is proposed. If the mean value of varying data rate at a specific cluster head is known a priori, then the routing solution obtained by the proposed algorithm achieves maximal network lifetime. Further, we prove that the routing solution is optimal by applying the bit rate routing algorithm, and the simulation results validate the effectiveness.