Abstract: In order to study the influencing factors and regularity of the conversion coefficient of self-balanced pile tested in expansive soil area, and to ensure the applicability of the self-balanced test method in expansive soils area, a numerical simulation on model test of self-balanced pile and traditional static pressure pile was carried out. The influence rule of the properties of expansive soil, geometric parameters of pile body and properties of pile-soil contact surface on the conversion coefficient of self-equilibrium method were analyzed by the method of controlling single variable. By the method of fitting, the quadratic term distribution formula and correlation coefficient between each factors and conversion coefficient were obtained. The results show that the conversion coefficient of negative friction resistance decreases with the increase of water content in expansive soil. The conversion coefficient decreases by about 0.2 when the water content of the expansive soil increases from the initial value of 18% to 30%, and the free expansion ratio and shear strength of expansive soil have large influence on the ultimate bearing capacity of piles. In addition, the conversion coefficient of negative friction resistance increases with the increase of pile length and pile diameter. Thus, it can be inferred that the negative friction resistance has less effect on large diameter and extra-long self-balanced piles.