Soil arching effect is the basis for retaining piles.In this paper,FEM is first used in the study of stress and deformation for a real soil arch,and then based on it,stress and deformation condition behind retaining piles for deep pit is analyzed.The soil behind retaining piles can be divided into 3 region:(1) the region under soil arch,(2) soil arching region,(3) uniform stress zone in crown arch.In region(1),the maximum principal stress is tensile stress;the stress state in region(2) is the same with that of the real soil arch.The boundary of these 3 regions is studied.The influence on the structure of soil arching region by loading and clear space of retaining piles is also discussed.