Abstract:A method of determination of reduced suction based on the principle of equivalence of deformation is introduced;and the reduced suction is used as an essential variable in the earth pressure calculation of unsaturated soils on retaining wall and swell increment. The rest soil pressure,active soil pressure,passive soil pressure of unsaturated soil under different water table conditions,and swell increment of unsaturated soil under different water level conditions and swell increment that are caused by rainfall have been considered. The calculation results have rationally reflected the distribution trend of unsaturated soil pressure and swell increment. Comparing the calculation results with the results of centrifugal model test and the model trough test,it is found that they have very good consistency. Calculation results also verify the proposed formulation.