Abstract: In order to obtain greater throughput, smaller packet loss rate and the average delay, research on carrier detection mechanisms, especially the collision back-off algorithm which impact on network performance was carried out. By analysis to several traditional algorithms, an improved collision back-off algorithm with node access fairness is proposed. With the design and implementation of the improved algorithm using NS2, simulation to WLAN performances was performed. Because that different window regulating competition strategy, according to a previous packet monitoring the collision situation, were used for sending stations and non-sending stations, the results showed that the algorithm not only ensures the fairness of data sending among stations, but also improves the performance of throughput, packet loss rate and packet average delay to some extent.