Abstract: In order to analyze the slope stability in consideration of the rainfall influences， it is necessary to couple the calculation of the rainfall infiltration and the slope internal force. Special characteristics of the unsaturated soils make the calculation more complex, because the soil′s hydraulic permeability and strength would change with moisture content. In the paper the principle of the effective stress of the unsaturated soils is introduced. The similarities and differences of the principle of effective stress and failure criteria used in the PLAXIS and Geo-Studio softwares are compared. In PLAXIS, the finite element method is used for unsaturated seepage calculation and a simplified Bishop effective stress formula is applied to the calculation of consolidation, deformation and slope stability. The constitutive models for the saturated soils can be used on that basis. The Geo-Studio uses the finite element method for the unsaturated seepage calculation and the limit equilibrium method for the calculation of the slope safety factor, in consideration of Fredlund′s bilinear strength criterion. Finally, details of the method for modeling the unsaturated slopes in PLAXIS are presented with calculation examples. The calculation examples show that the models in PLAXIS can accurately reflect rainfall-induced slope safety factor variation. Therefore, this software can be adopted for the unsaturated soil slope design and calculation in the future.