Abstract: To ensure the safety of internal dumping operations during the transition stage of open-pit mining, prevent slope instability caused by dip-oriented weak layers, and guarantee the continuous and long-term safe op-eration of coal production. This study focuses on an internal dump with a dip-oriented weak layer at the base in an open-pit coal mine located in Xinjiang. A refined three-dimensional geological model has been estab-lished using geological modeling techniques. Based on numerical simulations, the deformation character-istics of the slope have been systematically investigated under internal dump turning angles of 15°, 30°, 45°, 60°, 75°, and 90°, and the potential failure mechanism of this type of slope has been identified. Using the reduction factor method, the variation law of the slope stability factor for weak-layer controlled slopes has been further evaluated. The results indicate that the influence of the internal dump turning angle on slope stability is highly significant. The slope stability factor exhibits a logarithmic decrease with increasing turning angle. Larger turning angles lead to stronger weakening effects of the dip-oriented weak layer on the potential sliding mass, and the overall failure pattern is characterized as a combined bedding-parallel and bedding-shear sliding mode. The basal dip angle of the potential sliding surface increases approximately linearly, while the available dumping space volume increases approximately quadratically with turning angle. These findings offer valuable technical guidance for the design of internal dumping schemes in open-pit coal mines.