By analyzing the advantages and disadvantages of commonly used calculation methods and introducing a nonlinear pile-soil interaction model, a method for calculating the internal forces of cantilever piles was proposed, which can consider the pile-soil interaction. Firstly, finite bar elements were used to discretize the pile structures, and then, elemental stiffness matrixes were calculated and incorporated into global stiffness matrix. Secondly, the nonlinear function relationship between earth pressure and pile displacement in or out of the foundation pit was assumed, and then the nonlinear function array of joint loads was established. Thirdly, the overall stiffness equation was formed according to the global stiffness matrix and nodal load function array, and was solved to obtain the nodal displacement array by using the Newton-Raphson method. Finally, the internal forces of pile and lateral earth pressure were calculated with the elemental stiffness equations and nodal displacement array. The example analysis shows that the proposed method is simple and convenient, fully reflecting the characteristics of nonlinear variation of earth pressure acting on piles, and revealing the mechanism of pile-soil interaction well. Therefore, it is suitable for the internal force calculation of cantilever piles.