Annual net primary Productivity (NPP) in the Heihe River basin from 1998 to 2007 was estimated on temporal scale of ten-days from Spot VEGETATION NDVI dataset with modified CASA light use efficiency model. Changing tendency of NPP in the Heihe River basin from 1998 to 2007 was analyzed. Response of NPP to climate change for various land cover types in upper, middle and lower reaches was also investigated. Effects of water transfer project in the Heihe River and ecological construction on vegetation NPP change were quantitatively assessed after separating contributions of climate change and human activities. It was found that NPP of vegetated area experienced a significant decrease from 1998 to 2001, but it increased significantly from 2001 to 2007. Year 2001 is the key transition point of NPP change in the last ten years, coinciding with deployment time of water transfer project and ecological construction. During the 5 years (2002-2007) after implementation of water transfer project and ecological construction, the residuals of mean NPP for various land cover types in upper, middle and lower reaches are greater than 0, indicating that water transfer project and ecological construction have had a positive impact on ecosystem. The contribution rate of human activities on NPP in middle, upper and lower reaches was 11.5%, 5.29% and 3.23%, respectively.