Abstract: Based on the technical route of flash flood evaluation in Anhui Province, this paper investigates the his-torical floods and dykes in the Yuexi County section of Yaqian River, considers the design flood results of Yaqian River and the backwater effect of Maojianshan Reservoir, and determines the disaster water level and flow, so as to further deduce the warning threshold of rainfall. It is concluded that the warning water level of Yuexi Station is 366.30 m(300 m³/s), the guaranteed water level is 367.60 m(890 m³/s), and the critical warning threshold of 1 h is 80 mm; which provides technical support for effective prevention of flash flood disasters.