Abstract: Based on the modification of a seismic earth pressure theory for retaining structures under any lateral displacements, new formulas are proposed to determine the relationship of lateral soil-wall displacement and corresponding earth pressures against the sidewalls of the structure during an earthquake. The formulas can be extended to layered soils and deep foundations. A simplified mass-damping-spring model with the formulas is presented for dynamic interaction between layered soils and semi-buried structure. The model is feasible because parameters are easily obtained and no iteration is needed. The model is effective under the following conditions: 1) The soils behave as a visco-elastic medium; 2) The structure and its surrounding soil layers are represented as a group of shear beams which displace in horizontal direction only; and 3) The soil's response is not affected by the structure's movement.