In order to enhance the overall performances of wireless networks

this paper analyzes the influences of the binary back-off algorithm and the size of Contention Window（CW）used for the Distributed Coordination Function（DCF）of the Media Access Control（MAC）layer of IEEE 802.11 wireless networks in the fundamental working mode.It then optimizes the back-off mechanism by increasing the initial CW

cancel the Distributed InterFrame Space（DIFS）that busy channels need to wait for when they become idle but still have to be back-off and set up an intermediate value as a threshold so that different back-off algorithms are adopted when node transmission is a success or a failure.OPNET simulation results show that the improved algorithm can effectively reduce network access delay and improve the system throughput.