Abstract: In order to study the relationship between the depth of the weak layer and the stability of the soft rock slope, take a soft rock slope open-pit coal mine in Inner Mongolia as an example, based on engineering geological survey results and preliminary design, we determine the physical and mechanical indexes of rock and soil and establish a typical engineering geological model. According to typical engineering geological models, limit equilibrium theory is used to analyze the relationship between the depth of weak layers and the stability of soft rock slopes. The results show that if there is a weak layer of mudstone under the 10th coal floor of the mine, when the weak layer is located 20 m below the floor mudstone, it will have the greatest impact on the stability of the slope. Based on the research results, a weak layer survey plan and underground rock movement monitoring program are proposed.