In this paper,? Xiaanxi small watershed of Three Gorges reservoir area was taken as a case study. On the basis of the platform of GIS software, pertinent factors for soil erosion were assessed and three principal factors were identified as evaluation indices of soil erosion risk. The proposed principal factors include slope factor obtained from 1∶50 000 DEM, land use type factor and degree of vegetation coverage factor from SPOT-5 of 2008 remote sensing images. A soil erosion risky classification map was generated, which combines classification criterion on soil erosion. The amounts of soil-erosion for this small watershed were estimated and mapped using spatial analysis by GIS and an improved calculation model of soil erosion modulus. The result indicated as follows: (1) Soil erosion by water, a dominating type of erosion, accounts for 88.81% of total areas of small watershed, in which moderate erosion estimates for 38.49% of total area of small watershed. (2) Artificial erosion induced by mining made a great contribution to soil erosion amount of small watershed, which accounts for 61.92% of total soil erosion amount. Therefore effective soil and water conservation measure should be taken during engineering construction, such as mining and construction of foundation installations.