The interactive effects of gravel content and slope gradient on soil erosion processes of sloping farmland remain inadequately quantified, limiting predictive capabilities and effective conservation. This study investigated how gravel content, rainfall intensity, and slope gradient collectively influenced the particle size distribution of eroded sediment, thereby advancing the mechanistic understanding of soil erosion processes on sloping farmland containing gravel. Through simulated rainfall experiments, the results demonstrated that sediment yield was more sensitive to rainfall intensity than to other factors, and slopes containing gravel generally yielded more sediment than those without gravel. Fine sand, which accounted for 49%-56%, was the dominant fraction, with a clear coarsening trend observed under higher rainfall intensities. Critically, gravel presence significantly altered sediment structure, reducing the mean weight diameter (MWD) while increasing the fractal dimension (D). A key finding was the significant interactive effect (p < 0.05) between gravel content and slope gradient on particle sorting. The treatment with 20% gravel content and a 15 degrees slope gradient was identified as optimal, promoting the enrichment of clay and silt and suggesting improved aggregate stability and permeability. The findings reveal the complex role of gravel in erosion processes, highlighting its potential to exacerbate sediment yield under certain conditions. The results of this study provide theoretical and data-based support for the management and conservation of sloping farmland containing gravel in the Three Gorges Reservoir area.