Abstract: Until now the research activities in the field of unsaturated soils have been still in the academic stage.The key point of troubles is the measurement of suction.To avoid the difficulty in the determination of soil suction,the so-called reduced suction had been proposed recently.A method to determine of reduced suction based on the principle of equivalence of deformation was introduced,and the reduced suction was used as an essential variable in the calculation of earth pressure of expansive soils at rest on retaining wall.The results of calculation have rationally reflected the distribution trend of unsaturated soil pressure at rest.The proposed formulation was verified by the calculated results.