The channel exploration problem is analyzed for the distributed HF opportunistic spectrum access (OSA) system. Due to the scarcity of the spectrum resources, applying the cognitive radio technology to the HF communication system has called extensive attentions.Multiple secondary users (SUs) sequentially sense multiple licensed channels. Then the system decides whether the channels can be used based on the sensing results. Thus, the data can be transmitted utilizing available spectrum bands by using spectrum aggregation technology. However, the ability of spectrum aggregation is constrained by hardware limitations. Therefore, a dynamic stopping approach is proposed considering the interaction among the SUs under the constraint of the hardware limitations. In the proposed stopping approach, the channel-free probability can vary with the process of channel exploration and the SUs can periodically release the previously sensed channels. Moreover, simulation results show that the throughput performance of the HF communication system can be effectively improved by the proposed dynamic stopping approach.