In this paper, we proposed a backoff mechanism to improve the performance of initial ranging for the IEEE 802.16 standard. In the proposed scheme, the size of contention window in the initial ranging is combined with exponential and linear backoff mechanisms, and it is adjusted based on the current network environments. In addition, a threshold in the proposed scheme is set to find out the current network situation. If the contention window size is smaller than the threshold, the contention window size is tuned exponentially in response to a light network traffic load. On the other hand, when the contention window size is larger than the threshold, the contention window size is tuned linearly in response to a congested scenario. The numerical simulation results show that the proposed scheme can achieve a better performance in terms of collision rate, average access delay, and system throughput in both light and congested environments.