A dynamic frequency hopping channel access algorithm is proposed based on the hidden Markov model. It helps to improve the interference of primary users and secondary users, and the decrease of throughput. Long-time data transmission leads to the fact that secondary users cannot switch channels timely, so we divide the long transmission time into several frequency hopping periods, build the hidden Markov model to predict the available channels, set up frequency hopping channel set, and design dynamic frequency hopping sequence. Theoretical analysis and simulation results show that the algorithm reduces the interference of primary users and secondary users obviously, and improves system throughput effectively, and it increases system reliability and channel utilization.