Guaranteed quaIity of service (QoS) support has been an open issue of distributed wireIess networks for years. The IEEE 802.11e provides a vaIuabIe method for this purpose. However, it couId onIy provide service differentiation, rather than service guar-antee, for muIti-priority traffic. Many studies have tried to improve its QoS abiIity, but stiII Ieave some probIems. This paper investi-gates these probIems and proposes a scheme caIIed the priority access based on busy tone (PABT) to improve the QoS perfor-mance. To guarantee the priority channeI access, this scheme uses an in-band busy tone to Iimit the transmission of Iower-priority traffic when higher-priority traffic has packets to send. Based on that, it aIso optimizes the contention window tuning according to the flows number of each traffic type individuaIIy, in order to im-prove the throughput as weII as the traffic capacity. SimuIation resuIts show that the proposed scheme significantIy improves the reaI-time traffic capacity, throughput, deIay, faess and packet Ioss rate.