Abstract: The first phase of water supply project in northern Xinjiang belongs to seasonal water supply project, and the leakage of channel operation is serious for many years; what's worse, the sliding failure of channel slope is frequent. In order to further explore the sliding failure mechanism of canal slope, the mechanical properties of canal foundation soil are studied, and the numerical simulation analysis under different working conditions of canal slope is carried out by using the variation law of its strength characteristics. The results show that: Under the condition of wet-dry-freeze-thaw cycles, the shear strength c, φ values and elastic modulus E of expansive soil decrease seriously. The c value of white sandstone decreases obviously with the increase of water content, while the φ value is basically unchanged. The c and φ values of gobi material are not significantly affected by water content and cyclic conditions; During the water supply period, the sliding failure did not occur on the canal slope after multiple wet-dry-freeze cycles, which can be explained by that the normal component of hydrostatic pressure increases the anti-sliding force of channel foundation soil along the sliding plane, while the tangential component reduces the sliding force of channel foundation soil along the sliding plane, thus improving the safety and stability of channel slope; During the period of water shut-down, the coupling effect of wet-dry freeze-thaw cycle and water level behind the membrane leads to the sliding failure of the canal slope. The main causes are the attenuation of expansive soil performance, the softening of white sandstone under water and the change of pore water pressure caused by water level behind the membrane. The replacement of shallow soil, the optimization of stress structure and the reduction of water level behind the membrane can play a mitigation role; The existing drainage wells have no anti-slide effect on the canal slope, the local stability of the canal slope in the middle of the drainage well is the most obvious, and the single pile protection range is the largest, which is 44.3 % and 45 m², respectively.