Black soil shoal grassland is one of serious soil degradations in the Yellow River source regions. Large area mapping and monitoring of serious soil degradation is conducted typically using aerial sketch mapping and where necessary, ground survey. Both techniques have limited utility in wilderness areas where ground access is difficult and aerial mapping is too costly. Sub-pixel processing for analysis of Landsat Thematic Mapper (TM) imagery of Black soil shoal grassland was utilized and compared with survey. The study area was on Gande County, west part of Yellow River area in Qinghai province, west of China. Three dates of imagery were acquired and processed using Imagine Sub-pixel Classification software. The results were compared with existing limited ground survey data, and then three dates of result was compared. The sub-pixel analysis method can successfully detect Black soil shoal than using custom classification technology. Sub-pixel analysis can be an effective supplement to other means of soil degradation where the geographic extent of the degradation is too large for standard aerial sketch mapping techniques and dynamic surveying in cold and arid areas. The result also showed that the serious soil degradation extended very quickly, the velocity was about 3.4 percent every year.