The shallow landslide of highway slopes in areas with expansive soil often occurs. Three representative types of expansive soil from the south and north of China are tested under wet-dry cycle in the laboratory. The collapse of slope surface in low pressure conditions

and the conventional process of saturation and shear test are considered in the experimental study. The purpose is to obtain the actual shear strength of expansive soil and its reduction. The results show that the shear strength of the expansive soil affected by different vertical load is not identical. The larger vertical load results in the smaller reduction ratio of shear strength. The sectional double line method is adopted to approximately reflect the nonlinear characteristics of strength of expansive soil. It can also be used to calculate the index of shear strength c and ?. The c reduces exponentially as the number of wet-dry cycles increases

and it is considered as the main reason for the shallow landslide. ? decreases as the number of wet-dry cycles increases. The amplitude of reduction decreases. Under the same wet-dry conditions

the ultimate shear strengths of different expansive soils drop to a certain range. Research conclusion can provide reference for analysis of shallow landslide of expansive soil slope effectively.