Abstract: In deep foundation pit, soil wedge is assumed in an active state of limit equilibrium under the gravity effect of side wall. Anchors or other supports produce pressure to the wedge slip surface, thus intergranular stress, shear stress, friction and shear strength prevent the slope sliding. When digging deeper, soil can still maintain the state described above. Theoretical derivation was carried out according to this concept and More-Coulomb strength theory: the relationship between shear stress strength increment and the principal stress increment was obtained. And accordingly, the formulas of the maximum and minor principal stress increment and the internal stress distribution of soil wedge were obtained. The analytic formula for pit wall vertical depth with the lateral pressure and the foundation pit top load was established, which is suitable for generalized nonlinear strength criterion in soil test, and stress circle with shear stress envelope was drawn. Nonlinear internal force analysis method was provided. Compared with the current earth pressure calculation model, this method is material saving and has obvious economic benefit.