A unified analysis procedure is developed for the efficient and accurate design and analysis of bridge pier structures. The nonlinear pile group analysis method based on structural stiffness theory, was adopted for considering the pile-soil-pile and pile-cap interactions, and soil nonlinearity. It extended and then combined with the analysis routine of superstructure. Among the components of bridge pier structures, a pile cap is modeled with four-node flat shell elements and a pier with three-dimensional beam element and the pile-soil-pile interaction is considered by p-multipliers. A nonlinear analysis method is proposed with an incremental and iteration technique in this study. The proposed method for a bridge pier subjected to both axial and lateral loads is verified by comparing with existing computer codes (Group 5.0, FBPier 3.0). Through the comparative studies, it is found that the present method gives similar results with the other analysis codes about lateral displacements. The proposed method is capable of predicting the behavior of a bridge pier installed in nonlinear soils on the various loading conditions.