The paper discussed theory and methodologies of soil erosion assessment and established an implementation process according to USLE factors combining with thematic paper maps and DEMs. Factors of USLE-R, K, S,L, P and C were adapted to the test area, the Nihe Gou catchment in Chunhua County of Shaanxi Province, China. Afterwards the parameters of the USLE were evaluated individually and merged in order to calculate the amount of soil loss over the corresponding years, 1977 and 2003. In order to derive all necessary factors a TIN was generated out of a paper contour map. Furthermore, thematic paper maps and climate data completed the source of information for the implementation. The quantitative methodologies integrated with GIS were applied during the process. The verification of the result was performed comparing the real world situation at the test area with the resulting thematic maps. It shows these principles and methodologies were reasonable and feasible and can provide basis or reference for further areas of the Chinese Loess Plateau.