Machine to machine（M2M） communications had a huge potential market.Wireless local area network（WLAN） as the main complement for 3G networks would carry a lot of M2M services.Considering the characteristics of typical M2M small data service which was delay tolerant and retry patient

a large time-scale backoff algorithm was proposed in the network model of IEEE 802.11 DCF.MAC layer service time probability distribution was derived

and IPP/G/1/K discrete-time queuing model was established in order to analyze the QoS performance of M2M under unsaturated traffic condition and imperfect channel in the WLAN.Simulation results indicate that the proposed algorithm effectively enhances system throughput and reduces system blocking rate.