Based on analysis to the causes and laws of soil erosion in Zhaotong prefecture, Yun'nan province, the vegetation coverage percent, land use type and topography slope degree were selected as the key factors for evaluating the degree of soil loss. After fieldwork and analysis to the related materials, the relationship between TM image features and those key factors were established. And the vegetation coverage percent and land use type were extracted from TM accordingly. Combined with the information of slope degree from topography map, the erosion-grading map of Zhaotong prefecture was produced by ARC/INFO 7. 11 and ARCVIEW3. 2 software. Finally, according to the result of statistics from the erosion map, scientific evaluations on the ecological effects were made for the Changjiang river protection forest in Zhaotong prefecture.