As the development of wireless networks, no doubt it brings much more convenience to us. Besides, QoS (Quality of Service) demand emerges due to the popularity of multimedia traffic. Therefore, it is quite worthwhile to do researches about how to provide QoS in wireless networks. 802.11 wireless networks are the most widespread wireless networks currently, and the main goal of 802.11e task group is to support QoS. This thesis proposes a method for further improving QoS under 802.11e environment. According to varying ratio of CBR-like / VBR-like traffic, it adaptively adjusts the proportion of CP/CF medium access mode, and selects the corresponding admission control mechanism. The basic philosophy is to choose favorable transfer ways for different traffic characteristics, hence to reduce average delay. In addition to reduce average delay, we propose another mechanism to maintain or improve system throughput as well.