A comparative study of the reinforcement effect of conventional vacuum preloading method, graded vacuum preloading method and optimized graded vacuum preloading method is carried out through indoor model test. Through the comparative analysis of the change law of soil settlement, drainage and vacuum degree during the reinforcement process, and the comparison of the soil moisture content and particle size distribution curve indicators before and after reinforcement, the vacuum degree transfer law is worked out and the mechanism of different vacuum negative pressure strengths are analyzed. The results show that the optimized vacuum preloading method is better than the other two, and directly applying a large vacuum suction force (-80 kPa) after the first stage (-20 kPa) will not cause further blockage of the drainage plate and can improve drainage efficiency.