Abstract: The effect of the intermediate principal stress was not considered in the traditional earth pressure theories, which did exist and should not be neglected. Based on the unified strength theory considering the effect of the intermediate principal stress proposed by Yu Maohong in 1991, this paper deduced the equations that can be widely applied. The solution of Rankine is a special case of this paper. According to the relations between the undrained strength parameter and concreted undrained strength parameter, the formulae for earth pressure are deduced and analyzed by using effective stress method and total stress method, and the relation of the earth pressures under the two cases are got. At last, the paper contrasts the results of the unified solution with other papers published.