Abstract When mining coal under a loess gully, the surface slopes may exhibit significant discontinuous failure characteristics such as local failure and landslides. These characteristics, composed of failure and non-failure regions, form an essentially unstable mechanical system. This makes it difficult to obtain a true solution using continuous medium mechanics, greatly increasing the complexity of slope failure evaluation and management. To accurately evaluate the degree of slope failure during mining, clarify its mechanism, and propose appropriate management measures, the Ningtiaota Coal Mine in northern Shanxi was selected as the study area. Based on the unbalanced thrust method and the probability integral settlement prediction theory, and utilizing numerical calculations, we propose a method for evaluating and managing slope failure in coal mining under loess gully. This method describes the changes in slope failure during mining through the deformation failure ratio of the slip surface and quantifies the degree of slope failure at different mining times, revealing the full process stability evolution characteristics of points and surfaces as the critical state of the slope progresses. When the deformation failure ratio of the slip surface is ≥1, it indicates overall slope failure and the beginning of slope sliding instability; when the deformation failure ratio of the slip surface is <1, it indicates local slope failure. Based on this, corresponding management methods are proposed according to the mechanical distribution characteristics of the slope slip surface in different stress areas. The research results were applied in the Ningtiaota Coal Mine in northern Shanxi, yielding positive outcomes.