Vegetation plays a pivotal role in the interaction between the biosphere and the atmosphere.Previous studies have focused on monitoring changes in the fractional vegetation cover(FVC)on account of its important role in regulating the terrestrial carbon and water cycling during the past several decades.To revealthe effects and adaptation mechanism of climate change to grassland ecosystem in Three-River headwaters region(TRH),we firstly estimated FVC using SPOT-VGT datasets and dimidiate pixel model in TRH from 1998 to 2012.Secondly,the variation characteristics of annual FVC were analyzed.Discussions were finally carried out for the response on FVC to climate factors.The results showed that FVC of TRH during the past 15 years significantly increased(P<0.01)in the growing season,with an annual increase of 0.004 at the regional scale.For the types of alpine grassland ecosystem,the relationship of FVC with temperature of the growing season in alpine meadow was better than that in alpine steppe(for alpine meadow:r=0.802,P<0.01;for alpine steppe:r=0.515,P <0.05).Compared precipitation in May-July with precipitation in growing season,the former had the more key impact on FVC in alpine steppe,but there were hardly any differences for alpine meadow.