Abstract: In order to improve the design and calculation of laterally loaded single pile when the pile deflection is comparatively great, the calculation method of the deflection and internal force of the pile is proposed based on the sugrade reaction method, in which the limiting resistance of soil and the common expression of the coefficient of subgrade reaction are considered. Analytical and semi-analytical solutions for the pile shaft in the plastic and elastic zones of soil are presented, respectively, and then the relevant computer program is developed using the Fortran language. The computed results indicate that the displacement and the bending moment increase significantly when the loads increase. The pile head condition plays an important role in the distributions of the displacement and the bending moment along the pile shaft. When the pile length exceeds the critical value, which is almost not influenced by loads and the pile head condition, pile responses nearly do not change when the pile length increases. The maximum lateral displacement and bending moment can be effectively decreased by improving the mechanical properties of the soil surrounding the pile. The maximum lateral displacement decreases when the pile stiffness increases, while the maximum bending moment is hardly influenced by the pile stiffness. The computed values are in good agreement with the measured values from a field experiment, which means that the suggested solutions are reliable.