The sudden rise and fall of floods in mountainous areas often cause serious economic losses and casualties.Realizing flood forecasting for small-middle rivers is crucial in flood control and disaster reduction.To explore the applicability of the HEC-HMS distributed hydrological model in small-middle rivers in mountainous areas of Jiangxi province, a distributed hydrological model based on HEC-HMS was constructed in the Shushui river basin as the research area.The model was selected for parameter calibration, sensitivity analysis, and flood process simulation using 12 rainfall events from 2013 to 2019.The results indicate that the CN value is the most sensitive parameter among the model parameters.The predicted and measured values of the model show that the qualified rates of peak flow and peak time are both 91.67%, the qualified rate of runoff depth is 100%, and the certainty coefficient is higher than 0.7.It shows that the HEC-HMS model has good simulation results in the Shushui river basin, which can provide reference for flood forecasting in small and medium-sized river basins in mountainous areas of Jiangxi province.