Concerning the spectrum access problem in cognitive radio network, a new spectrum access strategy Based on users’ Requirements Dynamic Spectrum Access(BRDSA) is proposed based on multi- class users’ different band requirements. It is the first time to consider the different band requirements of primary users and secondary users, using channel assembling technology which can help the user to utilize the discrete spectrum. According to the proposed network model, the queuing theory and Markov chain model are used to analyze the transformation of system status. The simulation results show that the BRDSA strategy can greatly improve the spectrum utilization.