In order to explore the main sub-rainfall factors that cause soil erosion in the agricultural small watershed of the Three Gorges Reservoir area, the study selected the Shipanqiu small watershed located in the heart of the Three Gorges Reservoir area as the research area, and analyzed the distribution characteristics of erosive rainfall in 2019 and the variation law of sediment yield process in catchment A and catchment B under typical sub-rainfall, and the correlation analysis method was used to explore the main influencing factors of sediment erosion caused by sub-rainfall. The results showed that: (1) Of the 119 rainfall events for the whole year, 19 were erosive events, including 10 erosive moderate rainfall events. The erosive moderate rainfall was the most common type in erosive rainfall events. Rainstorm and above is the type that caused the largest amount of sediment in the study area. (2) In the typical moderate rain, heavy rain and rainstorm sediment yield events, the amount of sediment yield in catchment B was 5.13, 1.66 and 7.56 times that of catchment A respectively. The analysis of the sediment yield process of three typical sub-rains showed that the variation of sediment yield line in catchment B was more dramatic with the extension of rainfall duration. (3) The correlation coefficient of PI_n factors and the amount of sediment yield in the study area ranked as PI₃₀ > PI₁₀ > PI₁₅ > PI₆₀ > PI₅ > PI₉₀ > PI. Correlation analysis of various rainfall factors and the amount of sediment yield in the study area ranked as P > PI_n > I_n > I > T. There was a very significant positive correlation between the amount of sediment yield and the indicators P and PI₃₀ in catchment A and B. To sum up, when carrying out soil and water conservation work in the three Gorges reservoir area, it is necessary to strengthen the ability of monitoring and early warning response to soil and water loss in agricultural small watershed caused by rainstorm and above. P and PI₃₀ can reflect the impact of natural sub-rainfall on sediment yield in small watersheds of Three Gorges reservoir well. When estimating the rainfall erosivity of natural sub-rainfall, PI₃₀ can be used as the main reference factor. Compared with the traditional farming mode with simple structure, agroforestry-water complex ecosystem has a richer and more diverse structure, which can not only fully develop and utilize agricultural resources in small watershed, but also be more conducive to soil and water conservation, and it is also more adaptable to the changes of rainfall environment.