文中研究了我国一些典型膨胀土的微观结构特征，将膨胀土中的微观结构单元归纳为三种类型，并将由结构单元组成的微结构特征分为六种。讨论了微结构特征与膨胀势的关系。研究了膨胀土中的光滑裂隙面的特征，如物质组成、微结构定向性等，并将定向特征与力学强度建立了关系，由实测资料得到摩擦角φ随定向度的增加而减小的结果 In this paper, the microstructure characteristics of some typical expansive soils in China are studied. The microstructure units in expansive soil are classified into three types, and the microstructural features composed of structural units are divided into six types. The relationship between microstructure characteristics and swelling potential is discussed. The characteristics of smooth fracture surface in expansive soil, such as the composition of matter, the orientation of microstructure, etc., have been studied, and the relationship between the orientation characteristics and the mechanical strength has been established. From the measured data, the results show that the friction angle φ decreases with increasing degree of orientation.