This study took Shangnan County, located in the upper reach of the Yangtze River, as the experimental research area, using Quantitative Remote Sensing Model（QRSM. Digital elevation model (DEM) of the research area was constructed with a GIS software platform, with the gradient and slope length factor (SL) derived based on the soil erosion factor algorithm-specific software. The factors influencing the generation of the high precision digital elevation model (DEM) were analyzed. The accuracy and error of the produced DEM were also checked. In particular, the solutions to the derivation of the terrain pixel factor SL of water boundary slope, slope factor, slope length, slope length factor and concave point problem and reflux technology processing were developed. The results indicated that, in Shangnan County, the slope area located on the 15° to 25° degrees was 530.51 km2, accounting for 22.93% of the total area. The slope area on the 25° to 45° degrees was 1 083.32 km2, accounting for 46.82% of the total area. The slope area on the 15° to 45° degrees accounted for 70% of the total area. This area was the main cause driving the serious soil erosion in Shangnan County, this results of this study were consistent with the actual status of the study area. This research extended the application of the QRSM to the upper reaches of the Yangtze River, being meaningful for further monitoring and forecasting of soil erosion across the whole of the Yangtze River Basin. Our study is also valuable for soil erosion monitoring in other small catchments, both theoretically and practically.