To analyze the impact of groundwater on ground motion parameters,in this study,we selected three practical sites and used two real seismic waves as input ground motions for calculating the seismic responses of the soil layer in conditions with and without groundwater.We used a two-phase model and a single-phase model for the conditions with and without groundwater,respectively,and applied the finite-difference and artificial transmitting boundary methods.Based on the obtained horizontal acceleration time history,we extracted peak acceleration and response spectrum data.From our comparative analysis results,we draw the following conclusions:(1) The peak ground acceleration of site soil with groundwater is significantly lesser than that without groundwater. (2) The value of the surface acceleration response spectra of site soil with groundwater is greater than that without groundwater. (3) Due to the existence of groundwater,the characteristic period of the amplification factor response spectra becomes long.