Abstract: Aiming at the prominent instability problems of internal dump slopes in open-pit coal mines under water-rich soft rock basement conditions and the current lack of effective control techniques, this study proposes practical slope stability control measures through systematic analysis of typical slope instability problems in an open-pit coal mine. Taking a typical open-pit coal mine in the Northeast coal-bearing area as the research object, the historical landslide processes are deeply analyzed, and the current situation of internal dump slopes is investigated in detail. The back-analysis method of landslide is adopted to determine the mechanical parameters of the foundation, and typical sections are selected for numerical simulation to reveal the slope instability mechanism. On this basis, fully considering adverse conditions such as soft rock foundation and groundwater, slope stability control technologies are put forward. The research results show that the southern slope of the open-pit coal mine in the study area slides along the weak mudstone layer of the coal seam floor both before and after internal dumping, and the internal dumping foundation and waste materials are significantly affected by groundwater. The peak mechanical parameters of the weak mudstone layer of the coal seam floor before landslide are a cohesion of 0.14 kPa and an internal friction angle of 10.6°, while those after landslide are 0.1 kPa and 5.5°, respectively. The landslide mode of the southern slope is mainly “slump-sliding type” before the formation of the internal dump, and changes to “traction-slump-sliding type” after its formation. To reduce the influence of groundwater on the overall slope stability, it is recommended to arrange “#-shaped” blind ditches at the bottom of the stope. Meanwhile, a dynamic construction technology of stepped rolling dam is proposed, a multi-functional dam structure integrating anti-sliding, drainage and retaining protection is designed, and a dynamic construction process featuring “core positioning, bidirectional rolling and stepped progression” is developed. The research provides a feasible technical approach for slope control of internal dump under the foundation condition of water-rich soft rock.