Abstract: NDVI (the normalized difference vegetation index) is the most commonly used index for monitoringvegetation growth conditions and coverage. In this study, Landsat TM images were collected during the vegetation growth periods of September 2002 and 2015 in the mountainous area of the Shiyang River Basin’s upper reaches in the Qilian Mountains. The two periods’ NDVI were calculated and vegetation dynamics were analyzed by using ENVI 5.2 software. In addition, the images were analyzed using supervised classification and principal component analysis so that the areas and changes of vegetation types could be calculated. Results showed that vegetation areas with high, medium and low coverage had decreased in 2015 compared to 2002 by 18.4%, 13.4% and 10.1% respectively. Vegetation areas with extremely high and extremely low coverage increased by 0.5% and 26.6% respectively. NDVI results showed that the degraded and improved areas of vegetation were 6935.6154 and 6595.2834 km², accounting for 51.26% and 48.74% of total area respectively. Analysis of vegetation type areas showed that the area of arbor forest had significantly increased by 108.75%, while the areas of shrub forest and grassland had significantly decreased by 49.87% and 19.78% respectively. These findings show that forest vegetation in the upper reaches of the Shiyang River Basin has degraded over the 13-year period.