Abstract: The prevention and control of flash flood disaster in mountainous areas of China Southwest Researchers usually follow the idea of "rainstorm-flood-water level-inundation", mainly focusing on the impact of "water", but ignoring the role of "sediment". Affected by the sediment concentration of floods, small floods with major disasters often occur in these areas. Taking Shouxi River, a typical mountain river in Southwest Sichuan Province, as an example, based on HEC-HMS (The Hydrologic Engineering Center's Hydrologic Modeling System) model, on the basis of flood prediction, SPSS (Statistical Product and Service Solutions) software is used to analyze the correlation between rainfall intensity, underlying surface conditions, topographic factors and soil particle size and sediment yield in the basin. The results show that the most influential factor on sediment yield is soil erosion factor, reaching 0.261, and the least influential factor is rainfall intensity, only 0.073. In order to further estimate the sediment yield of the flood, the MUSLE (Modified Universal Soil Loss Equation) formula in HEC-HMS model is simplified, and the sediment yield estimation formula of the flood in the watershed is redefined according to the comprehensive weight of each influencing factor in the principal component comprehensive model. The research results have reference value for estimating the sediment yield of the floods of middle and small-sized river basins in mountainous areas.