Abstract: External dump is the inevitable outcome of surface mining. Because of the special landform, some open-pit coal mines in the middle and west of China build their dump sites on the loess base with gully development, forming the loess gully base dump with weak basement and extremely complex morphology. Its stability will become an important factor affecting the safe and efficient production of opencast coal mine. As a result, to study in Loess Gully basal dump deformation destruction of spatial evolution, in Heidaigou dump as an engineering background, based on discontinuous structural plane theory and strength reduction theory, considering the gnawing and climbing effect of undulating structural plane, the failure mechanism of loess gully basement dump was analyzed. Using FLAC^3D numerical simulation method, the spatial evolution process of the deformation and failure of the dump was studied, the landslide mode and landslide area of the loess gully basement dump were determined by analyzing the maximum displacement cloud map of each section and the position of the deformation zone during critical instability. The results show that the loess gully basement can be regarded as an undulation and unfilled structural plane, and the gnawing and climbing effect will be formed under the loading and shear of the dump, that is, the irregular surface landslide of the raised shear part will occur in the dump. T Under the dual influence of the dumping load and the morphology of the gully base, the upper rock mass of the slope deforms first, and then the middle and lower rock mass deforms under the extrusion. The deformation zones located on both sides of the north-south central axis extend to the Northern Slope bottom, forming a quasi-ellipsoid deformation zone, and finally evolves into a push landslide. The research results can provide technical reference for landslide warning and slope treatment of Heidaigou dump, and provide reference for slope stability study of similar dump.