Abstract: Vacuum preloading is widely used in soft soil foundation reinforcement because it is a mature technology. However, in the treatment of deep soft soil foundation, the conventional pressurization method tends to cause cracks in the soil at the boundary of the reinforcement area. As an alternative, the strategy with step vacuum preloading can effectively control the appearance of cracks in the boundary zone due to the graded growth of vacuum strength in stages. Therefore, FLAC3D software was used to establish the numerical models of the hierarchical vacuum preloading method, of which the rationality was verified by combining the field measured data. On this basis, the comparative analysis of initial vacuum strength and vacuum loading time on foundation deformation was carried out. The results show that the step vacuum preloading could effectively reduce the difference between the horizontal displacement of the dam foundation surface and the soft soil layer, which is conducive to controlling the occurrence of cracks. Among the step vacuum loading methods, Scheme IV with 10-40-85 kPa is more suitable for the foundation of this project. The above research results can provide reference for the popularization and application of the step vacuum preloading.