[Objective] The objective of this study is to analyze the spatial and temporal changes of vegetation NPP(net primary productivity) and carbon fixation and oxygen release in the three-river headwater region during the past 14 years in order to provide scientific basis for the ecological sustainable development in this area. [Methods] NDVI, meteorological data, the land-use data and the remote sensing data were collected. The spatial and temporal variations in NPP and amounts of carbon fixation and oxygen release were analyzed based on CASA model, carbon emissions model and Sen+Mann-Kendall model. [Results] (1) The mean value of NPP was ranged from 0 to 750 g/(m²·a), which accounted for 81.72% of the entire study area. The spatial distribution of average NPP presented a decreasing trend from southeast to northwest. And NPP in the lower altitude, rivers and dense woodland areas was higher than that in the alpine regions, which indicated that NPP was affected by altitude, rivers and land types. (2) The NPP showed an increasing trend in recent 14 years, with a growth rate of 7.26 g/(m²·a)(p>0.05). As to the inter-annual variation of NPP, about 23.64% of the study area showed a decreasing trend (2.3% of them p<0.05) while 76.36% showed an increasing trend (30.58% of them p<0.05). (3) As to the variation of carbon fixation and oxygen release, the cultivated land was larger than the forest land and other land use types. Variation of carbon fixation and oxygen release in forage land was small. [Conclusion] The alpine grassland ecosystem in the three-river headwater region was good, as it was less influenced by human beings. However, ecosystem in the low altitude, river and human activities intensive areas was complex and the locally degraded, and ecological environment in those regions need to be protected.