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Polling scheme is adopted in the Wireless Local Area Network(WLAN) standard IEEE 802.11e , but the IEEE 802.11e does not clarify the access mechanism and the definition of priorities is complex. In this paper a new priority-based polling scheme for QoS differentiation is presented based on 802.11e. The Quality of Service (QoS) classes are differentiated by two different access policies in polling scheme. For each station the traffic with higher priority such as key or real-time data can access the common channel on Exhaustive Service policy and the traffic with lower priority can access the channel on Gated Access Policy. After the higher priority traffic in all stations finish transmission in order ,then the lower priority traffic begins to be polled and transmitted. A mathematical model for the polling system based on imbedded Markov chain theory and the generation function was used to predict the mean information packet waiting time. The results of mathematical analysis and simulations show that the new scheme can differentiate traffic efficiently and guarantees better QoS and system stability .