In view of the problem that the conventional elastic method tends to overestimate the pile-pile interaction, the finite element method is applied to establish the shear stress equation of pile shaft for pile groups in the semi-infinite soil mass. The equation is decoupled by considering the pile-pile interaction in a approximate way, a simplified analysis method is proposed for calculating the pile shaft shear stress and displacement to implement the high-efficient analysis of large-scale pile groups. The problem of interaction between two piles and differential settlement of pile groups with flexible cap are analyzed; and then comparisons with the existing results are presented. Parameters analysis show that the interaction factor calculated by the present method is more close to the result given by a rigorous integral equation method, while slightly smaller than Poulos’s results. The differential settlement ratio of pile group with flexible cap in three cases are relatively close to the existing conventional result when the pile spacing is small; while with the increase of pile spacing, a slight difference occurs between the methods. The results show that the present method can greatly reduce the amount of calculation and can be applied to the efficient analysis of large-scale pile groups.