Abstract: Karst is a process and result of groundwater geologic function and one of bad geological phenomena to tunnel grotto construction. In combination with the construction of the large underground power plants in a karst region, the stability of surrounding rock mass is studied with 3D explicit fi nite difference method.This paper analyzes the influence of surrounding rock mass stability with karst on underground power houses, and evaluates the reinforcing effect of underground grotto group with filling up.