Abstract: Classical Rankine earth pressure theory is an important calculation of earth pressure theories. The issue of wall earth pressure will be regarded as problem of plane strain, so we calculate intermediate principal stress by generalized Hook's law in plane strain assumption. We determine principal stress in accordance with the principle of Rankine earth pressure. On this basis, the formula of Rankine earth pressure is derived when the expression of principal stress in double-shear unified strength theory is used. The solution based on classical Rankine active earth pressure theory is a special case of the unified solution. Finally, an example was given to carry on sensitivity analysis of five factors in terms of the design theory of orthogonal test. The five influential factors were considered including the cohesion, internal friction angle, intermediate principal shear stress parameter unit weight. So the effect of intermediate principal stress on the Rankine earth pressure calculation results was a critical factor.