［Objective］ This study aimed to comprehensively analyze the spatial distribution and dominant influencing factors of soil erosion in the Three-River Headwater Region for ensuring regional ecological security. ［Methods］The average erosion rate for four decadal periods from 1983 to 2022 was simulated using a regionalscale process-based erosion model，PESERA. The optimal Parameters-Based Geographical Detector（OPGD） method was employed to evaluate the explanatory power of individual factors on erosion rates and the interactions between multiple factors.［Results］The accuracy of PESERA modelling results was acceptable in the Three-River Headwater region（NSE = 0.53，R² = 0.69）. The spatial distribution of erosion rates showed a gradual decrease from south to north. Severe erosion［> 150 t∕（hm²·a）］，mild erosion［< 5 t∕（hm²·a）］，and slight erosion［5-25 t∕（hm²·a）］were mainly concentrated in the headwater area of Lancang River（southern part of the study region），the headwater area of Yangtze River（northwestern part of the study region），and the headwater area of the Yellow River（eastern part of the study region），respectively. Other erosion intensities were mainly distributed across the southern parts of the Three-River Headwater Region. The analysis of individual factor detection revealed that terrain relief（0.43）and precipitation（0.35）were the most influential factors. Interaction analysis indicated that the combination of precipitation and vegetation cover had the highest explanatory power （0.73），while the interaction between terrain relief and other factors considerably enhanced their effects on erosion rates.［Conclusions］Between 1983 and 2022，mild erosion was the dominant type of soil erosion in the Three-River Headwater Region. Temporally，erosion rates exhibited an initial increasing trend followed by a subsequent decline. The main factors affecting soil erosion in the region were terrain relief，precipitation，and vegetation cover. The findings can provide valuable insights for soil conservation and ecological protection in the Three-River Headwater Region.