Abstract: The vertical vibration of seismic wave attenuates faster than its horizontal vibration. Therefore only horizontal seismic force is considered in the mathematic model to analyze the failure of rock slope. The influence of length, buried depth and orientation of the structural plane to the failure of slope are analyzed respectively. It is found that when the buried depth and the length h/L are in a similar value, for a certain horizontal seismic acceleration a,the destruction of slope would be easier to occur with the increase of buried depth and length. While when the buried depth and length are keep in constant values, the failure of slope would become easier with the augment of horizontal seismic acceleration. Moreover, with the enlarge of inclination of structural plane, the tensile stress in rock masses would increase gradually. While the shear stress would boost at first and then decrease. This can be attributed to the reason that the failure of rock masses under earthquake would change from shear state to tensile state when the length and buried depth of structural plane are keep in constant. Moreover, according to the superstition principle of wave, the influence of length and buried depth to the dynamic response of slope under seismic loading is explored as well. The results can be referred to the assessment of seismic stability of slope.