Abstract: Three dimensional finite-difference program of FLAC3D was applied to study pile groups behaviors due to excavation-induced lateral soil movements,including two piles in a row parallel to excavation slope or in a line perpendicular to slope,four-pile,five-pile,3×2 and 2×3 pile groups.Comparing the response of a pile among pile groups with that of a single pile located in the same position on slope,the interaction effect in pile groups had been found.Namely,when piles were arranged in a row parallel to slope,the interaction effect between piles was insignificant,while in other arrangements,the existence of either a front pile(a row front piles) or a rear pile(a row rear piles) could all reduce the displacement and maximum bending moment of the adjacent pile,and when a pile was located in groups with small space or among a number of piles,the interaction effect would increasey significantly.These conclusions were explained by arching effects of soil between piles theoretically,and verified by a practical project.