Using Normalized Difference Vegetation Index (NDVI), Net Primary Productivity (NPP) and Gross Primary Productivity (GPP) data from 2000 to 2015 and combining with of human interference level, linear regression analysis and geographically weighted regression (GWR) analysis were used to compare and analyze the grassland dynamics and their driving factors in the Three-River headwaters region before and after the implementation of ecological construction projects. Results showed that:(1) spatially, human interference and NDVI, NPP and GPP had significantly regional differences, which all showed increasing trends from northwest to southeast, and the grassland NDVI, NPP and GPP values during 2006-2010 and 2011-2015 were significantly larger than that during 2000-2004. (2) Compared with 2000-2004, the NDVI, NPP and GPP values of grassland have been improved during 2006-2010 after ecological construction project, while NDVI, NPP and GPP values showed degrading tendencies again during 2011-2015. (3) In all human interference levels, 70% of the grassland was improved within 5 years after the implementation of ecological projects, and the area ratio of degraded grassland significantly decreased and that of the improved grassland showed significant increasing trend, indicating that the implementation of ecological projects has contributed to the improvement of grassland ecosystems. Especially in areas of severe human disturbance, grassland changed from 52.71% degraded areas in 2000-2004 to 84.95% improved areas in 2006-2010. (4) The main driving factors affecting the dynamic changes of grassland were distance to roads, distance to settlements, population density, drought, temperature and topographic slope, and the distribution of each influencing factor had obvious spatial heterogeneity. The study will help to provide scientific guidance and decision-making basis for grassland ecosystem restoration, management and strategy formulation in the Three River Source Region.