Abstract: A great number of problems in practical projects like retaining walls and foundation pits are under plane strain state.According to the formulas for the intermediate principal stress under the plane strain established by Mohr-Coulomb, SMP, spatially mobilized plane, Lade-Duncan, AC-SMP strength criterion and generalized Mises criterion, the formulas for the active earth pressure and passive earth pressure are derived in these strength criterions and extended to clay, the calculated active and passive earth pressures are compared with the measured data.The results indicate that the development degree of the intermediate principal stress has a significant impact on the earth pressure in the process of soil break.The calculated active earth pressure in the Mohr-Coulomb strength criterion is larger and the passive earth pressure is smaller than the practical one because the effect of the intermediate principal stress is not considered, and the design tends to be conservative.The calculated results by the criteria of SMP, spatially mobilized plane, Lade-Duncan and the AC-SMP strength are close to the measured data, among which the results by the AC-SMP strength criterion is much closer.The earth pressure calculated by the generalized Mises criterion is no longer appropriate to describe that on the retaining wall.When design the retaining structures under the plane strain state, appropriate formula should be chosen to consider the contribution of the intermediate principal stress so as to give full play of the potential strength of soil and to improve the economic benefits in project construction.