Abstract: Based on the unified strength theory and the shear strength of unsaturated soil in terms of two state stress variables, the unified solution of shear strength for unsaturated soil under the plane strain condition is derived by taking into consideration the effect of the intermediate principal stress rationally. Analytical solutions for unsaturated soil of the active earth pressure, the passive earth pressure and the critical bearing capacity for strip foundation suitable for any lateral pressure coefficient are presented by considering the intermediate principal stress, particularly different influences of high and low matric suctions. The analytical solutions obtained in this paper have very broad theoretical values. More choices can be made according to the actual engineering situations. The results show that in the low matric suction region, the passive earth pressure and the critical bearing capacity for strip foundation increase as the unified strength theory parameter and matric suction increase, while the active earth pressure decreases. In the high matric suction region, the passive earth pressure and the critical bearing capacity gradually decrease and reach some constants. The influence of over-consolidation ratio on the critical bearing capacity for strip foundation is less significant.