The maximum communication distance of main CSMA/CA protocol in present 802.11 communication protocol is only 300 m;and the system performance declines dramatically with the increase of distance over 300 m.The cause for this problem was analyzedand a method of changing ACKtimeout in accordance with the variation of distance was providedwhich improved the performance of CSMA/CA protocol in long distance communication.Simulation was carried out with OPNET softwareand the results showed that in long distance communicationsystem throughput is improved and connected delay is reduced.