Debris flow in Hongshui valley located in the upper area of Seregu hydropower station in Heishui County,Sichuan Province is studied.Based on the survey of the debris flow site,the formation conditions of debris flow and its dynamics features are analyzed and its hazard assessment is made.Results show that the material factor,rainfall factor,and physical feature satisfy the formation conditions of debris flow in the valley.The formation conditions are sufficient and the scale is medium.Its hazard degree is high and its development trend has been accelerated.