Using the daily meteorological and hydrological data, the HBV model is calibrated and validated for the Hejiang River Basin and the relationship between rainfall and discharge is established. Since the stagedischarge relationship of the Xindu hydrological station is built, the critical rainfall values corresponding with the three flood risk levels are obtained. The risk warning effectiveness is verified by applying the critical rainfall to two historical flood processes caused by heavy rainfall. The results show that the 24and 48hour critical rainfall values are important for warning. The calibrated HBV model can well represent the responses of hydrological processes to the rainfall, which provides references for Hejiang River Basin flood disaster prevention.