Abstract: Aiming at the difficulty of flood forecasting for small reservoirs in data-deficient areas, a flood forecasting model for small reservoirs was constructed. The SCS model was used in the runoff generation module, and the geomorphological instantaneous unit hydrograph (GIUH) was used in the confluence module. The model parameters were determined based on high-precision topographic and geomorphic data, rather than calibration with the measured flow data. The constructed model was verified by the heavy rainfall flood encountered by Yonggu Reservoir in Anhui province during the“Rumbia”typhoon （International number : 1818） . The application results show that the simulated values of the two flood peaks by the model were consistent with the values deduced by experts. The relative errors were 3.2% and − 11.8% respectively, both within 20%, and the peak time difference was 0. The relative error of runoff depth simulation is-19.2%, and the deterministic coefficient is 0.949. Hence, the small-scale reservoir flood forecasting model established in this paper has a good performance, and can give a good reference for flood forecasting of other small reservoirs.