Abstract: Based on Biot’s theory of fluid-saturated porous media, this paper presents the effects of groundwater level variation on earthquake ground motions through the analyses of wave propagation in layered foundation. In this analysis, a layered foundation model is built, assuming the saturated soil layer below the groundwater level as water-saturated porous soil, and the soil layer above the groundwater level as air-saturated porous soil. Numerical results show that under the incident P wave, the groundwater level variation has larger effect on the amplitudes of ground surface displacement, especially on the amplitudes of vertical surface displacement when the relative stiffness of soil skeleton is small. With the decline of the groundwater level, the vertical surface displacements increase, and the frequencies at the resonance peaks decrease correspondingly. But when the relative stiffness of soil skeleton becomes large, the variation of groundwater level has little effect on earthquake ground motions.