As one of the major issues in global environmental research, the impacts of climatic factors on regional vegetation variability has attracted widespread attention from scientists and it is important to understand the driving mechanism of this variation by using remote sensed data and meteorological observations. In this study, based on meteorological data in the period of 1980-2012,MODIS-NDVI data in the period of 2000-2012 and methods of linear regression and correlation analysis,our aim is to explain how climate changes impact on Qinghai and Tibet alpine grasslands since the 21st century. Results indicated as follows: (1) Qinghai and Tibet regions both showed warm and humid trends over 1980-2012. But in Tibet region, annual precipitation performed a decreasing trend with less significant in the period of 2000-2012. Warming trend was significantly throughout the central and western regions of the Tibetan plateau (>0.05 ℃·a~(-1)). (2) At the interannual scale (in 2000-2012),NDVI showed a significantly increasing trend in Qinghai region, with the rate of 0.003·a~(-1) (P<0.05). However, unchanged trend in NDVI was found in Tibet region owing to that vegetation degradation and recovery mutually offset at the regional scale. Spatial NDVI largely presented rising trends in northeastern of the Tibetan Plateau with the slope of 0.01·a~(-1),but in southern Tibetan Plateau, NDVI trends were worse at the slope of 0.008·a~(-1). (3) Regional correlation analysis expounded the different trends in Qinghai and Tibet regions. In Qinghai region, increasing precipitation and warming temperature together promote positive trends of regional vegetation. Reducing precipitation and rising temperature might be important reasons causing vegetation deterioration in the south of Tibet region.