This paper is mainly concerned with the saturated-unsaturated seepage analysis of earth dams based on unsaturated soil theory and the stability analysis of earth dams based on conception of slices. At first, beginning basic seepage theory, thesis introduce the saturated-unsaturated and steady-unsteady seepage differential equation of porous media and the FEM regarding hydraulic pressure head as basic unknown quantity. Then considering the shear strength of unsaturated soil, the method of analysis of general limit equilibrium has been approved and it can be used in the analysis of the stability of saturated-unsaturated slopes. Through an example it is respectively discussed effects of seepage flow when water head is changed in earth dam and the effects of percolation in the stability of the earth dam slope. Some helpful conclusions are gained. This can be making the best of the tow methods and the results can be used in engineering for reference.