To solve the problem that the spectrum allocation algorithm based on graph theory coloring algorithm has not fully considered the actual bandwidth needs of users, this paper proposes a spectrum allocation based on user priority algorithm improved CSGC and the original algorithm. The algorithm introduces two time factors that are respectively called idle spectrum and user demand, by setting the user priority, the function can meet the needs of users during the second spectrum allocation. Simulation results show that the algorithm not only retains the performance of the original algorithm CSGC, but also greatly improves the spectrum utilization.