An improved CASA(Carnegie ames stanford approach) model is used to estimate the terrestrial net primary productivity (NPP) in Three-river headwaters region.Results indicate that the NPP decreased from the southeast to the northwest,while the NPP in southestern area of Yellow River is higher than that of the Yangtze River.NPP shows a slightly downward trend during 2004—2008,with the maximum of 62.93 Tg·a^-1 in 2006,and minimum of 60.9 Tg·a^-1 in 2008.Seasonal variation of NPP is also prominent,which started to increase from May to July,then decreased gradually.The annual NPP of alpine meadow is 188.95 g·m^-2·a^-1,higher than that of aloine steppe of 129.41 g·m^-2·a^-1 in the region,while interannual variation of aloine steppe is increasing during 2004—2006.The analysis shows that temperature is the key factor controlling the terrestrial NPP in the region,followed by precipitation and total solar radiation.The NPP fluctuation in the higher elevations of this region is significantly related with temperature,with correlation coefficient being 0.8,while the correlation coefficient between NPP and precipitation is 0.7.