In this paper,according to the investigation data on geography,geology,hydrology,weather,vegetation,and flood disaster in Qilian Mountain area,critical rainfall amounts were determined using Case Investigation Method of Disaster,Frequency Analysis Method,and Rainfall Formation Analysis Method.In addition,Risk areas in typical river basin were plotted based on frequency of flood and flood peak volume,which could be used for flood disaster prevention and control in small river basin in Qilian mountain area,as well as for a research reference in similar river basins.