Abstract: Rainfall, especially the long-lasting heavy rainstorm, is a major cause of instability and failure of slope.During the rainfall, a large number of rain infiltrations will cause the slope soil saturation increases, the matrices suction of non-saturated region reduces and the soil shear strength decreases.When the rainfall intensity and duration exceeds a certain extent, it may lead to slope instability.Based on the discussion of unsaturated soil strength theory and percolation theory, the progress of unsaturated soil slope stability research in recent years was discussed.