Abstract: The spatial distributions of disasters in Taipei Basin and Sichuan Basin are different. A series of two-dimensional plane strain models for sedimentary basins, the cross sections of which are simplified to isosceles trapezium, are established to analyze the seismic response of sedimentary basins and to study the major influencing parameters of basin effect. It is concluded that because of the reflection of seismic waves at the boundary of basins, contrasted to horizontal layered sites, the seismic response of basin sites makes a large difference. The standard deviation of horizontal acceleration may rise by 150%, and the standard deviation of vertical acceleration is corresponding to that of horizontal acceleration in magnitude. If the size of basins is relatively large, the basin effect just has a relatively distinct impact on the seismic response of the edge of basins, and the incidence is approximately equal to the projected length of the inclined bedrock surface at the edge of basins, concluded by the standard deviation of horizontal acceleration, or triple of that, concluded by the standard deviation of vertical acceleration. The maximum standard deviation of acceleration increases with the increase of the depth of basin sites. The maximum standard deviation of horizontal acceleration remains virtually unchanged and that of vertical acceleration reduces with the increase of shear wave velocity of soil.