Abstract: Based on the twin shear unified strength theory，the unified solution of Coulombs passive earth pressure for unsaturated soils was deduced by considering the influence of intermediate principal stress and the matric suction，etc． Through comparing the calculation results of the proposed formula with those of the unified solutions of Ｒankines passive earth pressure，the rationality of the proposed formula was verified． Additionally，the effects of parameters on Coulombs passive earth pressure were discussed，including the intermediate principal stress，the matric suction and the friction angle． The results indicated that the unified solution of Coulombs passive earth pressure for unsaturated soils had very broad applications． The Coulombs passive earth pressure of saturated soils and the Ｒankines passive earth pressure of unsaturated soils just were the special cases． The intermediate principal stress，the matric suction and the friction angle had significant influence on the Coulombs passive earth pressure，and the Coulombs passive earth pressure increased with the increase of unified strength theory parameter，matric suction and friction angle．