Abstract: The shear strength of soils is an important theoretical basis for the design and analysis of geo-structures in the engineering practice. For the unsaturated soil, because its microstructure is more complex than that of the saturated soil, the shear strength is more difficult to determine. To determine the shear strength of the unsaturated soil, many scholars have studied the microstructure, the expression form and the measurement of unsaturated soils. Among them, the soil-water characteristic curve is of the great significance, and the soil will have obvious influence on the soil-water characteristic curve after the dry and wet cycle, which is an important basis for studying the shear strength of unsaturated soil. To deepen the understanding of the shear strength of the unsaturated soil, the current progress of the shear strength research of the unsaturated soil was described by the reviewing many literatures, and the shear strength formula in recent years was summarized, and the direction for future research was suggested.

Key words: Unsaturated Soils, SoilWater Characteristic Curve, Shear Strength