Abstract: According to the concept of lateral equivalent load and the classical variation principle in elasticity, the present work deduces a symmetric matrix for the P-Δ effect to revise the stiffness of long piles. Meanwhile, considering the distributed horizontal soil resistance, a method of setting lateral nonlinear spring s, which is very applicable in finite pole element analysis, is proposed based on the concept of Newmark spring and the p-y curve formula. Then, a nonlinear finite pole element analysis model for a single long pile under inclined load is established based on the above improvements. The relevant finite element program is compiled on the basis of the analysis model and applied to real projects. The correctness and feasibility of the proposed model is confirmed by comparing the results of this study with those of the pervious approaches, testing piles and simulations. Moreover, the influence degree of P-Δ effect is analyzed.