Abstract: A 3D model for a rock bedded slope considering groundwater fluctuation is established by the finite difference software FLAC^3D. Firstly, the hydromechanical coupling effect is considered on the basis of the dynamic response and a dynamic pore-pressure model, and the acceleration response of this seepage slope under the seismic action is studied. Then a brief analysis of the groundwater effects on the distribution of the plastic zones of the slope was made. The numerical simulation results show that the peak ground acceleration (PGA) amplification coefficients and the acceleration of the top of the slope are greater than those of the slope without considering groundwater fluctuation. As the groundwater level rises, the values of PGA amplification coefficients and the slope acceleration of the top of the slope are in the fluctuation conditions. However, when the whole slope is in a saturated state, two parameters mentioned above (i.e., the PGA amplification coefficients and the acceleration of the top of the slope) increase substantially. The acceleration of the toe of the slope also fluctuates as the groundwater level changes and a significant increase also occurs when the whole slope is in the saturated state. Moreover, the PGA amplification coefficient isoline distribution of the seepage slope is more 'messy' and has worse regularity than that of the slope without considering groundwater. The contour of the seepage slope still obviously reflects the vertical acceleration amplification effect and free face acceleration amplification effect. In order to analyze the damage conditions of the slope, the distribution of the plastic zones is analyzed. It is found that the plastic zones are mainly distributed in the surface weathered layer. Moreover, the plastic deformations are caused by the tensile shear interaction with the rising of the groundwater level. It proves that the damage effects of the groundwater under the seismic action on the slope increase. Comprehensive analysis of the acceleration response, the displacement of the slope top and the distribution of the plastic zones show that the groundwater is unfavorable to the seismic stability of the bedding rock slope.