Abstract: In order to study the influence of long-term rainfall on the southern slope of an open-pit coal mine in Xinjiang, and the variation of pore water pressure in the slope at different periods after rainfall, Darcy’s law and Van Genuchten model and numerical simulation method are used to analyze the stability of the existing slope after rainfall; the research results show that: under the influence of long-term rainfall, the pore water pressure in the south slope of the stope changes little, while the positive pore water pressure appears in the upper slope. The long-term rainfall makes the underground water level rise, the cohesion of the slope decreases, and the shear strength decreases, which leads to the transient safety system of the slope.