Abstract: Based on the effects of atmospheric enviroment on macro-microcharacteristics of expansive soil, the comparative tests on shear strength characteristics between the undisturbed soil and the pile-soil interface were carried out on the middle expansive soil in Nanning area, Guangxi in order to investigate the infulence rules of variation of soil properties on behaviours of the pile-soil interface in expansive soil foundation under the environment of moisture migration. The results show that the moisture content has more significant impact on the strength of expansive soil than that of the pile-soil interface in path of the moisture absorption. The cohesive strengths of both the soil and the interface decrease with the increase of water content, and the effect on the decrease of friction angle of expansive soil is much greater than that of pile-soil interface. The friction angle of the interface is always larger than that of the soil, and less affected by changes in moisture content. When the water content of expansive soil is close to the saturation, the strength of pile-soil interface is approximately equal to that of the soil. Through regression analysis, a relational expression for the shear strength of pile-soil interface is obained by the dicription of strength parameters of expansive soil. Correspondingly, the strength of pile-soil interface in expansive soil foundation can be predicted by using the soil strength under the environment of natural moisture absorption.