As an important part of the alpine pasture on the Qinghai-Tibet Plateau, the alpine desert grasslands, which are assumed to be sensitive to climate change, are suffering from rising grazing intensity. However, due to the lack of data, the relative impact of climate change and grazing on the growth of alpine desert grasslands is still in debate. Ritu County in Ali area of Tibet is located in the transition zone between the monsoon and the westerly zone. The most typical vegetation type here is alpine desert grasslands. In this study, based on data of the satellite-derived normalized difference vegetation index (NDVI) during 2000-2016, we analyzed the relative impacts of climate change and grazing on NDVI changes for Ritu County. Data of air temperature, precipitation and standardized precipitation evapotranspiration index (SPEI) were used as indicators of climate change, and those of livestock (LN) were enrolled as a key indicator of grazing. The results showed that:1) NDVI tended to increase during 2000-2016, which is associated with the variation of temperature, precipitation, SPEI and LN. And LN seems to exert relative larger impacts on the variation of NDVI. 2) Partial correlations indicted that LN was a main driving force for the variation of NDVI before the launch of the ecological restoration project (Grazing Withdrawal Program, GWP) in 2000-2007. However, the main driving force shifted to SPEI since the GWP started (during 2008-2016). The results indicate that alpine desert grasslands are vulnerable to grazing activities and climate change. The impacts of climate change and grazing on vegetation differs between different time scales or space scales. By controlling the number of livestock and therefore reducing the pressure of grazing, the GWP effectively suppressed the significant decrease of NDVI in grasslands and wetlands in Ritu County.