Abstract: The inner dumping site of Haerwusu Surface Mine has several negative factors of slope stability. Dump space needs to be increased, the water flows from end slope into the dump site, the foundation and dump materials have the same inclination. By studying the foundation lithology and bad geological conditions of inner dump site, according to the failure mode of the waste-dump, 7 potential failure modes of inner dump are analyzed, the landslide model of inner dump is determined by the sliding along the abandoned material and the weak layer on the base, the main factors of controlling the increase of inner dump site are the weak layer between 5 m to 10 m in the lower part of the foundation.