Abstract: Since most of expansive soil slopes exhibit shallow landslide, undisturbed and remoulded expansive soils of Nanning outer ring are specially selected to carry out contrast tests. Through the well-designed test program, by improving the conventional sample preparation conditions and methods of direct shear tests, laboratory simulation of soils under seasonal drying shrinkage and wetting expansion is made closer to the actual situation. Meanwhile, the rules of strength reduction of the two kinds of soil samples subjected to wetting-drying cycles are studied. The results show that the strength reduction ratio of the soil samples with loading is smaller than that of the soil samples without loading after experiencing the same wetting-drying cycles, which verifies that the loading has an obvious inhibitory effect on the shear strength reduction. Whether it is undisturbed or remoulded samples, the strength reduction is mainly owing to the decrease of c after experiencing wetting-drying cycles and the reduction of φ is not obvious. Moreover, taking the low stress of slope shallow layer sliding into consideration when conducting tests, by analyzing the test results, reasonable shear strength parameters can be determined to analyze the stability of shallow slope. The research conclusions can be used for reference in engineering design.