[Objective] The main factors affecting soil erosion in upper reaches of the Ganjiang River basin were analyzed, in order to provide a reference for local soil erosion control and scientific management.[Methods] The data involved in this paper including Landsat 8 remote sensing image in 2015, MODIS NDVI, digital elevation model (DEM), soil type and rainfall. The RUSLE model and the random forest algorithm were used to quantitatively analyze soil erosion and its influencing factors in the upper reaches of the Ganjiang River basin.[Results] In 2015, the soil erosion intensity was gradually increased from southeast to northwest in the upper reaches of the Ganjiang River basin, and the soil was at a mild erosion level in general. The total amount of the soil erosion was 3.45×10⁷ t/a. The average soil erosion modulus was 1 046.38 t/(km²·a), which was about two times higher than the allowable amount of soil erosion 500 t/(km²·a) in the red soil hilly region of Southern China. The average soil erosion moduli of sub-basins 9, 11 and 15 were 1 672.66, 1 715.83 and 1 565.36 t/(km²·a) respectively, which were at a moderate erosion level. These sub-basins were the key regions which need to be prevented and controlled in the study area. The rest of the sub-basins were under a mild erosion level.[Conclusion] Soil erosion in every sub-basin was greatly affected by the vegetation cover and management factor (C) and the slope length and slope (LS), and the importance of which was 30% and 20% respectively. The importance of soil erodibility factor (K) and the rainfall erosive force factor (R) were less than 10%. Among all sub-basins, sub-basin 9, 11, and 21 were mainly affected by LS factor, and the rest were mainly controlled by C factor.