Abstract:The plunge pool slope of a hydropower station in construction in Southwest of China is influenced by atomization-rain according to the forecast distribution of atomization-rain caused by spillway flood discharge. The slope is liable to fail in the form of horizontal-push landslide on the condition of rainfall based on the research of fissures combination and forces loaded on them. The block in the slope,which is made up of G222–2 as bottom slip face and f556–1 as back tension fracture,is liable to slide when the underground water level is 772.1 m high according to the calculating results of the start criterion of horizontal-push landslide. A seepage model of the underground water in the slope on raining condition is established to analyze the relationship between underground water level,and the time of raining for the underground water mainly comes from rainfall and atomization-rain. Results of calculating show that the start criterion is reached if there are rainstorm over 260 hours or both rainstorm and atomization-rain over 246 hours. And the horizontal-push landslide is to happen. In order to keep the slope safe,measures such as slope protection should be taken to isolate the rock from water.