In this paper, we propose an autocorrelation-based transmission power control (A-TPC) method to increase the transmission reliability and reduce the energy consumption. In A-TPC, data packets from multiple sensor nodes are scheduled in the TDMA-fashion. The transmission power level and the slot scheduling are jointly optimized based on a temporal autocorrelation model. The channel datasets collected from real WBAN daily scenarios are imported into our simulation model to evaluate the performance of A-TPC. Simulation results demonstrate that A-TPC significantly improves the transmission reliability and reduces the energy consumption.