With the advantages of convenient communication and low cost, wireless sensor network (WSN) is widely used in many areas for information collection, and LEACH protocol is one of the routing protocol used in WSN. Therefore, optimizing LEACH protocol can improve the performance of WSN, including the speed, lifecycle and coverage. The optimization of LEACH protocol mainly focuses on improving network energy efficiency, reducing node energy consumption, improving ways to select cluster head nodes, and extending network lifetime. On the basis of extending the network lifetime, this paper optimized the energy allocation and choosing cluster heads. With our method, the new energy threshold is established, and the nodes whose energy is lower than the threshold is not eligible to compete for cluster heads. The amount of cluster heads that can minimize the total energy consumption of the network is found, as well as the optimal P- value is confirmed. The threshold formula for selecting cluster heads is optimized. The final results of simulation show the optimized node death time is significantly later than that before optimization, which can prolong the network lifecycle of LEACH protocol.