Abstract: The canal of expansive soils is in the state of wetting-drying cycle because of seasonal water level fluctuations, and its slope instability is easily induced. The centrifugal model tests are carried out to study the stability of a canal slope of expansive soils under wetting-drying cycles, and its failure mechanism is investigated. It is found that the soil of the canal slope undergoes various wetting-drying cycles due to the repeating water level fluctuations in the canal. After each cycle, the cracks in the soil gradually expand, the water in the canal infiltrates continuously, and the saturated area gradually increases. The stronger the expansive capability of foundation soils, the more severe the crack extension after each wetting-drying cycle, the stronger the infiltration of canal water, and the more easily the canal is destroyed. The main failure mode of the canal caused by wetting-drying cycles of water level fluctuations is shallow instability, which is quite different from the retrogressive landslide discovered by other researchers.