Abstract A Xiaozhai landslide numerical model is established by Geostudio software, which is then used to study the stability and seepage characteristics of a landslide at different rainfall conditions and stages. The results show that: the destabilization process of this landslide can be divided into three stages.In the first, Qel + dl4 accumulates;in the second, contact zone (stratum between mudstone and quaternary eluvium) weathers through meeting with water;in the last, the weathered zone is softened and thickened under the humid environment. The formation and development of the softened weathered zone is closely related to highly permeable slide mass and low-permeability slip-bed that is the determining factor of a landslide; The reason a landslide is triggered can be ascribed to low permeability of mudstone, which prevents rainwater infiltration and promotes rainwater enrichment in contact zone. As the rainwater enriches, the weathering of mudstone accelerates and forms a highly weathered weak bed layer. After a severe rainstorm, the weak zone will creep and a landslide happen.