This paper presents the design, analysis and performance evaluation of a algorithm, called Adaptive backoff mechanism. This algorithm is based on the relationship of length of queue and network traffic and the duty cycle. The basic idea of this algorithm is changing the size of the contention window according to the flow, thus relieving network traffic in high contention level and reducing the time of overhead in low contention level. Finally, analyzed through the NS2.35. The results showed that it is better than using a random backoff mechanism of SMAC protocol in the network delay, energy consumption and throughput.