Abstract: Wireless devices using different communication protocols share the same unlicensed frequency band. The communication frequency is overlapped between different transmission pairs. Thus, the transmission pairs interfere with each other. In order to achieve better communication efficiency and network capacity, coexistence of multiple devices using different protocols is studied in this paper. All communication pairs should do the attitude cooperation when developing the media access control strategy. In the unlicensed band environments, we propose a distributed and dynamic algorithm for the spectrum allocation. This algorithm randomly allocates spectrum to the wireless devices with different protocols. And the communication pairs update their operating channel in each timeline round. Finally, it can make the different devices distributed uniformly in all parts of the unlicensed spectrum. By fully utilizing wireless resources, the unlicensed band network capacity improves accordingly. In addition, the term‘scanning factor’ is presented in the paper, which leads to lower communication overhead of the algorithm. Moreover, the reduced control frames can decrease the communication interference between neighbor transmission pairs. In the end, simulation results show that this algorithm can dramatically improve the overall efficiency of network capacity. Furthermore, it guarantees end to end fairness between different transmission pairs to a certain extent.