In order to fill the gap in the understanding of offshore ground motion by topography， numerical simulation is used to analyze ground motion characteristics of common offshore slope sites. This paper combines the self-made seismic wave program and finite element dynamic analysis software ADINA to establish different slope site models， and analyzes the influence of topography and incident angle on the response of offshore site. This paper compares the site response and response spectrum characteristics of different slope site models to determine impact of terrain on ground motions. The results show that when P-wave is incident， site amplification effect of slope sites on the ground motion is related to site slope， and site amplification effect increases with site slope， which is quite different from seismic response law of onshore sites. When SV-wave is incident， slope sites has no obvious influence on seismic response of offshore site.