Abstract: The wetting-drying process caused by seasonally running of canals can significantly reduce the strength of expansive soil below the canal structure, thereby affecting the stability of expansive soil canal. Taking the typical expansive soil canal in North Xinjiang as an example, the mechanical properties and the development characteristics of surface cracks of expansive soil below the canal structure were studied in the direct shear laboratory with wetting-drying cycles. On this basis, the numerical calculation of the canal slope stability during the water-level falling period was carried out. The results show that with the increase of wet-dry cycles, the cracks on the surface of the tested soil samples are growing and gradually stabilized after a certain number of cycles. The cohesion of the samples decreases significantly, while the internal friction angle decreases in a small fluctuating manner. After five wetting-drying cycles, the cohesion and internal friction angle decreased by 36.5%~48.2% and 26.1%~10.8%, respectively. Additionally, with the increase of running years (wetting-drying cycles), the canal slope stability decreased year by year. The drainage time also has a significant effect on the canal slope stability. The longer the drainage time is, the higher the canal slope stability is. It is suggested that the drainage time of the expansive soil canal slope would better be more than 12 days, and the interval between diagnosis and maintenance would better be no longer than 5 years. The research results have a certain reference value for the construction and maintenance of water supply projects in Xinjiang.