Abstract: Based on the unified twin shear strength theory , and the problem of the interaction between the retaining structure and soil being taken as the spatial problem, the formulae of the active and passive earth pressure for clay and non cohesive soil are derived, and the influence of the weighted coefficient on the active earth pressure is discussed. To verify the feasibility of the proposed formulae, the results determined from the proposed formula are compared with those obtained from the experiment, also with those obtained from Rankine’s theory. It is shown that the active earth pressure determined by Rankine’s theory is larger than those obtained by the proposed formula and the experiment. When b=0.5, the results determined from the proposed formulae are in good agreement with those obtained from the experiment. So the proposed formulae have some guidance significance for the design of the retaining structure.