The water level falling of the reservoir produces saturated-unsaturated unsteady seepage in the slope. The unsteady seepage is one of the important reasons of slope instability. To know the influences of unsteady seepage on the slope stability

consolidation equation of solid and liquid phase porous media is derived

which takes the coupling role of seepage and deformation into consideration. On this basis

slope stability factor is calculated by finite element shear strength reduction method; and a set of unified finite element method is adopted for seepage

deformation and stability analysis. The influences of permeability of soil and falling of water level of the slope on stability factor of landslide in case of sharp falling of reservoir level are analyzed through case dies. The calculation results indicate that the theory and method proposed are feasible and effective. An efficient tool to analyze the slope stability problem under saturated-unsaturated unsteady seepage is given.