Abstract: To understand the status a of grassland degradation of Maduo County in 2009, a remote sensing assessment model between the grassland degradation index and vegetation index was established, further, according to the survey of grassland resources in the 1980s and 1990s, the dynamics of grassland degradation in the past 20 years was analyzed. The resulsts showed: (1)The weigh of plant height, vegetation cover and biomass were 0.21,0.39 and 0.40 among evaluation index.(2) MSAVI significantly correlated with grassland degradation index compared to the other vegetation index. The model can be quantitatively expressed as:Y=1.02+0.5 ln X. (3) Grassland area of Maduo County is about 2.22 million ha in 2009, and the area of grassland degradation is 1.76 million ha, accounting for 79% of the total area of grassland. Most of the grassland degradation were mild and moderately degraded, accounting for 66.5% of the total area of grassland. (4) With the establishment of the Sanjiangyuan Nature Reserve and a large number of ecological protection and construction project implementation, grassland degradation changed from the most severe and moderate in 1990s to the degradation of most mild and moderately degraded. Severe degradation had also been improved to the level of 1980s. However, the continuous expansion of grassland degradation is still. Area of grassland degradation increased from 1997 to 2009 by 15 million hectares amounted to 10% during 12 years.