The characteristics of vegetation and its response to climate change were explored using NOAA/AVHRR(NOAA/Advanced Very High Resolution Radiometer) (1982-2001) and EOS/MODIS (Earth Observation System/Moderate Resolution Imaging Spectroradiometer)(2000-2008) NDVI (Normalized Difference Vegetation Index) products, monthly air temperature and precipitation of Maqu, Madoi, and Xinghai meteorology stations over the source region of the Yellow River. The results showed: The vegetation of Madoi region generally revealed a decreasing trend in the time and space scale; the vegetation of Maqu region, which is the source region of the upstream Yellow River, revealed an increasing trend before 2000 and appeared to degenerate after that; The vegetation revealed a decreasing (increasing) trend before (after) 2000 in the north of the source region of the upstream Yellow River. The NDVI appeared to decrease during 1982-1990 in the spatial scale, this occurred in the east region of the Ngoring Lake. The areas with decreasing trend of vegetation further enlarged during 1991-2000. During 2000-2008, an evident degeneration occurred in Maqu area, while the vegetation of Xinghai region generally increased. The responding relationship of the vegetation to climate change implied: The air temperature was the most sensitive factor to vegetation variation in the source region of the Yellow River, an exponential relationship existed between them, the NDVI had a little variation when the air temperature was lower than 0.0 ℃, and the NDVI increased fast with the air temperature when the air temperature was greater than 5.0 ℃. Local precipitation had great contribution to the early growing of the vegetation, when the vegetation saturated and the NDVI reached maximum, local precipitation was not sensitive to vegetation variation anymore.