Abstract: In this study, theoretical equations of vertical impedance for single piles are deduced based on Hamilton’s principle. Reasonable calculation method for pile-to-pile interaction is proposed considering the vibration difference with respect to propagation direction. Finally, the impedance of pile group is solved by combining the deformation coordination condition and mechanical equilibrium of piles and cap. Parameter studies are carried out to investigate the topography effects on the dynamic impedance of pile group in sloping ground with various pile slenderness ratio, pile-soil modulus ratio and pile spacing. The results show that interaction factor and pile group impedance fluctuate a lot with frequency. The extent of topography effects depends on frequency and could be significant at specific frequencies The difference between the impedances for the pile groups in sloping ground and horizontal ground increases as slope angle, pile length, and soil stiffness increases, which indicates that neglecting topography effects may bring considerable error to dynamic impedance of pile group in slope.