Abstract: The significant spatial heterogeneity of the mountainous basin′s surface is a crucial restrictive factor affecting the accuracy of runoff calculation.Based on the spatial heterogeneity of the mountainous basin′s surface and its vertical transfer characteristics, we proposed a dominant runoff identification framework, which integrates vertical spatial heterogeneity through a four-tier system of soil texture, soil bulk density, topographic slope, and land use.Hydrological response units (HRUs) dominated by a single runoff component were delineated using GIS spatial analysis techniques, and a distributed runoff calculation model was developed.The Xiagushan Hydrological Station control basin in the Huaihe River was chosen as the study area, and the model was validated with data from 20 flood events from 1980 to 2021.The results indicate that runoff components in the watershed are distributed as follows: saturated overland flow (33.00%), Hortonian overland flow (0.80%), interflow (34.27%), and groundwater flow (31.93%).The relative error absolute value of the average runoff depth of the model is 11.12%, and the coefficient of determination is 0.98, indicating that the calculation results are relatively reliable.This study verifies the rationalities of the proposed runoff identification method, HRU delineation, and the development of the runoff calculation model, offering a novel approach to runoff calculations in mountainous flood events.