Based on the analysis of reasons for the poor reinforcement effect and the limited strength growth of dredged soil foundation with a high viscosity content after the conventional vacuum preloading, large scale model tests of graded loading vacuum preloading and conventional vacuum preloading are carried out, and the influence and advantage of graded vacuum preloading in the consolidation and deformation of convective clay are discussed. The results show that: the dredged fill mud is in a muddy mixture state with obvious fluidity, and the staged loading vacuum preloading adopts the initial small vacuum load and lasts for a long time. It is beneficial to slow down the prematurely accumulation and consolidation of soil around the drainage plate, and can give the full drainage and consolidation time to soil far from the drainage plate, which is beneficial to the improvement of the whole soil. The power consumption is only 60. 8% of the conventional vacuum preloading, thus it has high practical applicability and economic benefits.