The equilibrium differential equation and the corresponding boundary conditions of laterally loaded long-piles under double-parameter foundation on double-layered soil were deduced by means of energy variation principle. Meanwhile, the condition of moment equilibrium, shear equilibrium and the continuity condition of displacement and corner were used to relate the medium ground of layered soil. The coefficients of piecewise displacement function were derived by substituting the solution of equilibrium differential equation into the conditions of moment equilibrium, shear equilibrium and the continuity condition of displacement and corner, thus identifying the displacement curve of laterally loaded long-piles.Case study indicates, the stiffer layer on the earth surface can exert an influence on the displacement of pile, and as the diameter increases to some extent, its effect on the displacement of the pile is smaller.