Abstract: The interactive dynamic equilibrium equations of pile group-soil-structure system in time-domain are derived. The characteristic response of pile-soil-structure under vertical seismic s-wave is analyzed comprehensively by means of dynamic interactive factors of pile-to- pile which can be used to obtain impedance of pile-groups. The effect with various taking out-collocation of pile-groups on dynamic response of system is emphasized and evaluated on numerical computation, and some helpful conclusions are also obtained. In addition, a new design idea on pile-supported structures subjected to horizontal seismic load is presented with referring to the concept of settlement optimization which has been applied to vertical static analysis of soil-pile-structure systems.