In ordinary structural design practice, the seismic load is calculated by fixed-base condition based on the notification of Building Standard Law in Japan. However, building structures are actually constructed on a stiff and/or flexible soil, they are affected on soil-structure interaction (SSI) effect. The SSI effect is consist of two phenomena, i.e. “inertial interaction” and “kinematic interaction”. The natural period of building structure and the damping is changed by former phenomena, and the input-loss to structure during earthquake is appeared in latter phenomena. A finite element method (FEM) analysis or a sway-rocking (SR) model is generally used to consider this SSI effect. It is necessary that free ground analysis, impedance analysis and foundation input analysis for the construction of the SR model. The objective of this study is to describe a characteristic of a SR model.