Abstract: The non−persistent random multiple access wireless sensor network can control the system and reduce the energy consumption, but its effect is general and its practicability is not strong. This paper presents a WSN protocol of the variable collision length with three clock based on N−CSMA, by dividing successful packet transmission time (1+a), collision packet transmission time (b+a), idle packet transmission time a, in order to get the system throughput rate, collision rate, idle rate, packet transmission delay such important system parameters. By changing the value of collision length b, the average power P_n of the nodes is reduced, and the service life T of the business nodes is prolonged, so as to reduce the damage frequency of the business nodes and achieve the purpose of reducing the system cost. Finally, the correctness of the theoretical analysis is verified by simulation experiments, and the performance of the non−persistent protocol, 1−persistence protocol and p−persistence protocol are compared and analyzed.