Abstract: To predict the effects and influence circle of a soft foundation improved by vacuum preloading in Nansha Port of Guangzhou, according to the deformation characteristics of large area soft foundation improved by vacuum preloading , the method which considers the smear effects diminishing the permeability of the soil in the smear zone can be transformed into the reduction on horizontal permeability coefficient of the soil in the effective zone, is presented based on the equivalent consolidation degree. The pre-processing work of 3D FEM can be reduced and the smear effects are taken into account, and the influence on the consolidation degree induced by the size of element is discussed. Regarding soil as porous media and combining the project of vacuum preloading in Nansha Port of Guangzhou, a large-scale 3D FEM model is set up and the numerical calculation is executed with Biot consolidation theory. The calculated results agree well with the monitored data in situ.