At present, the mandatory contention resolution that shall be supported by IEEE 802.16 is based on truncated binary exponential backoff algorithm. In this paper, the differences of contention mechanism between IEEE 802.16 and IEEE 802.11 are analyzed. The calculations of performance metrics such as the utilization of transmission opportunity u, the delay of bandwidth request d and the drop probability of bandwidth request pd are presented. Based on simulation results, the effects of contention parameters such as the initial window W, the number of subscriber station n and the number of transmission opportunity Nto are discussed. Some policies to adjust the parameters are also provided. These policies are useful for BS to schedule its uplink bandwidth resource.