Abstract: Because of the special loess geological condition of the dump in Haerwusu open-pit mine and the plenty ponding water between the main dam and dump,it brings bad influence to the slope stability of the dump.We used FEPG software to discuss degeneration damage caused by ponding infiltration、capillary water,it revealed the overall process which weak layer turned into aquifer,we came up with a conclusion that coefficient stability would decrease under the circumstance of being infiltrated and the solution came out as to satisfy the production and safety requirement for the coal mine.