Unmanned Surface Vehicles (USVs) usually operate in coordinated formation and exchange data through wireless ad hoc networks due to mission requirements, and the channel transmission loss of maritime ad hoc networks is usually in a dynamic state owing to the influence of ocean waves.However, the existing backoff algorithm of MAC protocol in ad hoc networks cannot distinguish between packet collision and packet loss in a dynamic maritime environment, resulting in the decline of reliability and stability.Here, we propose an adaptive minimum contention window backoff algorithm based on channel monitoring.The algorithm estimates the channel state by sensing the number of adjacent contention nodes, reduces the channel collision probability and retransmission times, thus improves the reliability and stability of the network as a whole.Simulation results show that compared with classical BEB algorithm, the proposed backoff algorithm increases the throughput and fairness by 28.67% and 62.00%, respectively, and reduces the end-to-end delay and packet loss rate by 2.84% and 15.10%, respectively.