<p>Current research findings suggest that a narrow excavation's failure surface between adjacent cantilever retaining walls should follow a broken line pattern. The retaining wall rotates around the zero point of displacement and deflects, causing differences in the horizontal displacement along the wall. This leads to partial mobilization of the mechanical strength parameters, soil friction, and wall–soil friction. Evaluating the relationship between these parameters enables us to understand better how the earth pressures vary, and relevant formulas have been proposed. In a narrow foundation pit, the passive zone soil is squeezed by the retaining walls on both sides. Under the influence of wall–soil friction, the principal stress deflects and leads to a soil arching effect. Using this theory, the passive earth pressure coefficient and sliding surface's inclination angle can be derived based on the static equilibrium condition of the sliding wedge in the passive zone. The soil wedge is then divided into three zones, and a lateral pressure calculation model is presented. The level differential layer approach is utilized to obtain the pressure distribution along the retaining wall. Theoretical calculation results indicate that passive earth pressure increases with depth but decreases rapidly when approaching the zero point of displacement (in a non-ultimate state). Above the zero point, the displacement and deformation of a flexible wall lead to a smaller height of non-ultimate area and a more significant increase in pressure in lower soil layers. When comparing cantilever retaining walls with the same displacement and deformation state, those in narrower foundation pits experience greater passive pressure. Overall, the presented theoretical approach of calculating passive earth pressure distribution closely aligns with existing model test results and finite element method solutions.</p>