Abstract: Based on the nonlienar dynamics model of a single pile subjected to transverse excitation, the frequency-response equation of the primary resonance of the pile foundation is obtained by employing the motion equation of the pile and the method of multiple scales. Using the Vlasov foundation model and the empirical method to determine the pile group interaction coefficients, the modified elastic foundation parameters can be obtained. The influence of pile group effect on the nonlinear response of pile groups is examined by means of the frequency-response curves, the evolution of transverse displacement and the change of shear force of piles. Meanwhile, the effect of the boundary conditions on the pile group effect is also investigated. The results show that the pile group effect leads to complex behavior that exists in the primary resonance response of piles. Moreover, the influence of pile group effect on the dynamic response of piles is closely related to the main factors such as the boundary condition and the positional relationship of piles.