Abstract: Based on the IEEE802.11 DCF, an adaptive back-off algorithm to adjust contention window is presented. The basic idea of the new algorithm is that using nodes network allocation vector(NAV) information predicts the contending condition around it since the node will choose an adaptive strategy to compute the value of the contention window regarding to different network traffic. Results obtained from analysis and simulation show that the adaptive back-off algorithm increases the channel utilization and makes an improvement to the packet latency compared with the traditional back-off algorithm BEB.