A Dynamic Spectrum Allocation(DSA) method is proposed to solve the problem of low utilization of wireless spectrum resources based on Modified Cloud Quantum Genetic Algorithm(MCQGA). The method can adjust the rotation angle of the quantum gate dynamically, and uses the cloud theory to cross and mutate. According to the graph theory coloring model, the maximum sum of mean reward, the maximum minimum bandwidth and the maximum proportional fairness measures are considered for spectrum allocation. Particle swarm optimization algorithm, traditional genetic algorithm and basic quantum genetic algorithm are selected for comparative simulation experiment. Simulation results show that the proposed method is more suitable for spectrum allocation.