Abstract: The passive pile has received high attentions in recent years.This paper presents a systemic three-dimensional numerical analysis for the complicated interaction between pile and soil under preloading.The paper establishes 3D model using FLAC(3D) for the working property study of single row piles.The effect of some key parameters on the interaction is mainly researched.They include preloading condition,stiffness of pile and soil distributing.Based on the results of numerical analysis,the interaction mechanism between passive pile and soil in soft clay is further expatiated,and a linear distributing pattern of soil pressure along pile is obtained with a linear curving method.