It is well known that the acceleration response of the soft ground subjected to strong earthquake motion will be small due to softening of the ground. However this is inconsistent with the facts that the larger the earthquake damage is on the softer ground. In order to study the relationship between the seismic response of the ground and the earthquake damage, we performed centrifuge model vibration tests by using one dimensional shear column. The surface ground response is the input motion to super structures as well as the output response of the surface ground. From first point of view, it is found that soft ground plays an isolation role on short period super structure. From the second point of view, we have studied the frequency dependency of the shear stiffness of soft clay layer.