Abstract: Seismic wave propagation in a typical mountain-valley bridge site was studied based on the explicit finite element method with artificial transmitting boundary.The topographic effects of the incident degrees,the incident directions and the span of the mountain-valley were also discussed.It was shown that the amplification effects at the bottom of slopes did not change obviously.However,the effects near the top of slope were magnified to some extent.The absolute amplification factors were the largest under the condition of normal incidence,and the difference of the relative amplification factors at the left and right sides was not obvious.The normal incidence condition could be considered and the results were safe.Meanwhile,there was obvious directivity of topographic effects.The amplification effects were related to the span of mountain-valley.