Abstract: Based on the basic equations of elastodynamics and FEM, the time-domain integration by the Newmark method is used to handle the response of dynamic model, and the sub-structure condensed method is introduced to solve the boundary condition. The attenuation characteristics of ground vibrations in the upper-soft lower-hard ground and in the upper-hard lower-soft ground without pile group are analyzed. The dynamic responses of group piles and the ground near the piles are also calculated in the upper-soft lower-hard ground. The characteristics of frequency spectra for the ground vibration with group piles are analyzed. It is shown that the ground vibration isolation by group piles is noticeable.