Abstract: There are multiple water outlets in the dumping process of inner dump in Yimin Open-pit Coal Mine. In order to ensure the safe production of open-pit mine, the seepage path of groundwater inside the slope should be found out and the influence of groundwater on the stability of the slope should be analyzed. Through the analysis of hydrogeological conditions, the theoretical analysis of the physical effect of groundwater on rock and soil mass, and the experimental study on the influence of water on soil strength parameters, it is concluded that the increase of water content has a significant weakening on the strength of foundation mudstone and discarded material in the dump. Based on the numerical simulation of the groundwater seepage law in the two states of dump, present and design, the influence of groundwater on slope stability is obtained. According to the results of seepage analysis, comprehensive prevention and treatment measures for leading-drainage, centralized extraction and compaction and plugging of slope groundwater in the inner dump were proposed.