Part of mountain areas in Dayi county, Sichuan province, was hit in a catastrophic torrential rain and the rainstorm led to seriousmountain hazards-debris flows and landslides during the middle of September, 1998. Two persons were killed, one missed, and properties of over fifty million yuan was lost in the hazards. The genesis and the followed development tendency of mountain hazards were analysed through topography, geology, torrential rain and mankind economic activities. In conclusion, suggestiones in mountain hazards prevention and control are put forward.