Alpine grassland is the main vegetation type in the source regions of the Yangtze and Yellow Rivers, and accounts for about 70% of the total area in this region. As a result, maintenance of ecosystem balance, water cycling and soil-atmosphere exchanges in these regions critically depends on the status of the local alpine grasslands. With current global changes such as climate change, and increased human population in the region, alpine grassland in this region has been subject to increasing grazing pressure with significant changes resulting. These environment and regional economic changes have attracted widespread attention. In this research, alpine grassland degradation in the source regions of Yangtze and Yellow Rivers was quantified by analysis of images obtained by aerial photography in 1969 and TM remote sensing data captured in 1989, 2000, 2007 and 2013. In addition, with the inclusion of climatic observation data and data on human factors, the causes of the degradation were analyzed by principal component analysis and the gray correlation method. The results show that the alpine grassland degradation is characterized by reducing coverage, and increasing fragmentation and desertification. The total area of mid-cover alpine grassland and high-cover alpine grassland has decreased by 16.33% from 1969 to 2013. With a trend to increase in periodic drought, the total area of alpine meadow has decreased by 3.75% during the same time. Fragmentation and separation of alpine grassland units in the landscape has been occurring and also shrinkage and disappearance of patches. The rate of degradation increased very rapidly after the 1980s, and reached its maximum in 2000, but has been consistently decreasing since 2000. Climatic drought caused by a warming trend has been the main driver for alpine grassland degradation in the source regions of Yangtze and Yellow Rivers, and overstocking and unreasonable human activity were important contributing factors, intensifying the degradation.