[Objective] Constructing a flood forecast model of Qingshitan Reservoir to provide a reference for actual forecasting business, and also to provide support for the study of hydrological and meteorological laws in the area, e.g., Guilin City, where information in the upper reaches is lacked.[Methods] HEC-HMS(hydrologic engineering center and hydrologic modeling system) is a hydrological model system with multiple production and distribution modules. It is suitable for the analysis and calculation of hydrological problems in different areas. It is widely used in flood forecasting, disaster prevention and mitigation. This model was used in hydrological modeling of the upper reaches of Qingshitan Reservoir in Guilin City, to simulate the flooding process of Qingshitan Reservoir in the event of heavy rainstorm in the watershed as a basis for flood forecasting.[Results] The average deterministic coefficient of HEC-HMS model was found to be 0.88 by the study. The peak flow rate and peak current error all reached Grade B prediction criteria.[Conclusion] The HEC-HMS model is suitable for the Qingshitan basin and can be used for the flood forecasting of the Qingshitan Reservoir.