Dynamic interaction effects of a giant pier-pile group-soil system are investigated by a stochastic seismic response method. A complex response technique is employed in this method. The interaction system as an integrality is modeled by some finite elements and the dynamic nonlinearity of soils is considered through the equivalent linearity method. Stochastic seismic analysis of the free ground and the interaction system are carried out respectively; and their results are compared. The comparisons indicate that the effects of interaction are related to the modulus variance of pile and soil

and the distance of soil and pile foundation. The dynamic shear strains of soft soils have significant difference. The distributions of shear strains near the both boundaries of pile group appear to be curved. The peak acceleration values of ground surface and superficial layer obtained from seismic interaction analysis are smaller than that obtained from seismic free ground analysis. But

the peak acceleration values of deep layers have increases of 5%-30%. In addition

the frequency components of ground surface motions have marked difference for seismic responses of free ground and interaction system. Therefore

the dynamic bridge structure-pile group-soil interaction should be considered properly for the seismic design of bridge foundations.