A new method for the study of lateral dynamic interaction factors was presented by considering the participation of axial loads on pile-head in layered-soil in order to further extend the applications of the simplified S-R model in engineering practice. By means of substructure theory, the dynamic response of pile-groups-structure characterized by random configuration, pile number, soil properties, etc., can be fulfilled with less cost-time than other numerical methods. With the computation for a bridge-pier base suffering earthquake action, it is indicated that additional displacement will engender the effect of vertical oscillation, which results in the decrease of horizontal impedance effect of pile-groups, and the influence of pile-soil-pile interaction is markedly enhanced over that under single horizontal vibration. In general, the horizontal dynamic response of a whole system will be reduced due to the relative flexible participation of pile-soil subsystems.