Abstract: The p-y curve method for single pile under horizontal load is applied in excavation engineering. An elastic sugrade reaction model considering nonlinear interaction between protection-structure and soil for deep excavations is put forward. Above the pit plane, a computational model cansidering the protecting structure-soil nonlinear interaction is adopted; under the pit plane, the protection-structure is regarded as laterally loaded piles and the weight of soil above the pit excavation is applying to the protection-structure as an overloading. The differential equation of the elastic subgrade beam to consider the nonlinear interaction is derived based on the equation of the general elastic subgrade beam. The internal force and deflection of supporting piles are calculated by adopting finite difference method.