Abstract: The Lushan-Jizhong area in the upper reaches of the Shaying River in Pingdingshan City has complex and diverse geomorphology and geology, and has been repeatedly hit by flash floods over the years, and is one of the three major rainstorm centers in Henan Province. Taking the Jizhong river watershed in Tuancheng Township of Lushan County as the research object, firstly, the daily rainfall and flow monitoring data of the corresponding stations in the past 30 years were collected and analyzed. Secondly, different typical flood processes were selected to analyze the influence of soil moisture in the early stage on the flood peak flow and peak occurrence time of the three elements of the flood process. Finally, based on the HEC-HMS hydrological model and ArcGIS platform, the watershed of Jizhong river was divided into seven sub-watersheds, combined with the corresponding land use and soil data, the initial loss and steady infiltration method is used for the generating runoff calculation, the Sneider unit line is used for the collecting runoff calculation, and the Muskingum method is used for the riverine flood routing calculation, the typical rainstorm and flood processes in the watershed are numerically simulated. The results show that the early soil moisture has a significant impact on the flood process; the relative error eligibility rate of the flood peak of this model’s runoff generation and convergence plans is 89.25%, the eligibility rate of the relative error of flood volume is 86.6%, and the Nash coefficient is 0.821, indicating that the HEC-HMS model has good applicability in the watershed of Jizhong river. This study can provide reference for flood simulation in similar watersheds.