Abstract: To deeply discuss the mathematics model for EDCF (enhanced distributed coordination function), the performances of two access mechanisms, 802.11 DCF (distributed coordination function) and 802.11e EDCF, were analyzed and compared through simulation. The differences between 802.11 DCF and 802.11e EDCFwere discussed, and the principle of EDCF providing the quality of service (QoS) was investigated. Simulation result shows that EDCF can provide the guarantee of QoS forwireless LANs (local area network), but systemperformance deteriorates if there are many data streamswith high priority contend for a channel.