Following the rapid development of wireless networks, IEEE 802.11 technology has become the most widely used wireless network access technology. The contention channel of the distributed coordination function (DCF) is the default mechanism, which is used to determine the waiting time required before sending data. Once any collision has happened, the contention window expands to prevent future collisions, whereas when data has been successfully transmitted, the contention window shrinks to reduce backoff time. Determination of the increase or decrease of contention windows has become a vital to the transmission performance of networks. Through experimentation with different numbers of stations and different contention window sizes, this study found a collision rate range with superior efficiency, and thus proposed a collision rate-based backoff algorithm (CRBA). The proposed algorithm adjusts the contention window size according to collision rate, achieving enhanced efficiency and a reduced collision rate. According to the analysis of experimental results, the CRBA outperformed other relevant channel contention mechanisms (BEB, EIED, LILD, and ELBA) in terms of throughput, collision rate, and channel utilization rate.