[Objective] The stability evaluation of an open-pit mining area was carried out in order to provide technical support for landform remodeling, ecological environment restoration, and soil erosion monitoring in a mining area. [Methods] The ArcHydro hydrological model and watershed self-similarity principle were used in this study. The stability of geomorphic forms in an open-pit mining area and in the surrounding undisturbed area was evaluated using the geomorphic information entropy evaluation index. The risk of soil erosion and erosion intensity in the mine area were also determined. [Results] The geomorphic information entropy of the Hesigewula open-pit coal mine area in Inner Mongolia was affected by a series of processes such as stripping, mining, transportation, and disposal, and was mostly concentrated in the index value range of 0.105—0.145. The geomorphic system development of the watershed in the mining area was mostly in the juvenile stage or middle-aged to juvenile stage. The risk of watershed erosion was high. Most of the information entropy of the original landform and undisturbed area was greater than 0.40, where the watershed geomorphic system was stable and strong, with flat terrain and small soil erosion modulus. [Conclusion] The risk of soil erosion gradually increased from south to north at the Hesigewula open-pit mine due to the original landform of the mining area, the mining sequence, and the location of the dump site. The results of this study can be used as the basis for landform reconstruction and ecological environment restoration of similar open-pit coal mines.