Abstract: The stability of canal slopes of expansive soils is the premise of normal operation of water supply projects in Northern Xinjiang. Taking the water supply project in the high and cold region of Northern Xinjiang as an example, the canal slopes at expansive soils are destroyed obviously under the action of alternate wet and dry, freeze-thaw cycle, which is mainly manifested as the reduction of slope integrity caused by the cracking of shallow expansive soils and the deterioration of internal mechanical properties of the basic soils, which seriously affects the overall stability of the canal slopes of expansive soils. Based on the field measured data of the failure section of expansive soil canals, combined with centrifugal test results and interface theory in composite materials, the shallow failure mechanism and reinforcement measures of canal slopes of expansive soil are studied. The results show that the cracking of shallow expansive soils is the decisive factor causing the failure of shallow canals, and the specific failure is different from that of the traditional traction landslides, which mainly exhibits the failure of spalling of shallow expansive soils along the canal slopes. In addition, the continuous water loss process of expansive soils results in the conversion of strong bond contact between soil particles to weak bond contact, and causes the propagation path deflection of expansive soil cracks after they develop to a certain depth, and the cracks penetrate into the shallow soils, finally causing shallow damage to the expansive soil slopes. On this basis, it is suggested that the protective measures should be taken to reduce the cracking of shallow soils after the slope repair, and the anti-sliding retaining reinforcement measures should also be taken in time when the tensile crack appears at the back edge of the canal slopes.