When using FLAC3D which based on finite difference method (FDM) to calculate the seepage，the seepage surface is higher than the real situation’s and the permeability of unsaturated zone is a constant which is defined by mistakes. An adjusting element permeability method is used to develop the program secondly

and the modified adjusting element permeability method is proposed to correct the permeability of unsaturated zone strictly. After calculation

the exact continuous smooth seepage surface and saturated-unsaturated seepage are obtained. The FEM is used to analyze the seepage contrastively

and the feasibility and effectiveness of the method are validated. The method of attaching interface to downstream side is proposed to solve the problem in which the seepage points are hard to obtain on complicated three-dimensional boundary; then a three-dimensional complicated example is given to calculate the seepage field distribution of a slope; the result is accurate after verifications. The research results are helpful to guide the analysis of saturated-unsaturated seepage and the calculation related to seepage in the program.