Vegetation net primary productivity (NPP) is considered a key factor of ecological responses to climate change, so it has long aroused attention from countries around the world. Using the middle-lower Area of the Min river as the study area, the Geodetector model was applied based on MODIS NPP products from 2000 to 2015, as well as annual altitude, temperature, precipitation, and land use date in the same period to diagnose the dominant factors of spatial distribution of vegetation NPP change and reveal the different time changes of driving forces determining vegetation NPP differentiation. The results showed that 1) The average annual NPP for the middle-lower Area of the Min river was 513.93 gC/m² from 2000 to 2015. The maximum and minimum values (1876 gC/m² and 26.98 gC/m) observed in 2000 in the Qiaoqi Tibetan township north of Shimian county and 2005 in the plain dryland distribution area of Zhugen Town in the middle of Wutongqiao showed a strong spatiotemporal variability in the middle-lower Area of the Min river. In addition to the NPP intensity, the total area covered by vegetation was the other major influencing factor. 2) The dominant factors affecting vegetation NPP spatial distribution included temperature, altitude, and land use, and their power determinant value to NPP incidence differentiation. 3) These factors affect the changes in vegetation NPP from different perspectives and their driving forces differ over the years. The changes in vegetation NPP mainly presented more and more concerned by human disturbances. On the contrary, it is weakened by natural factors. Spatiotemporal changes of NPP and its driving forces were revealed. The findings provided the data and assistant decision-making for the government to formulate policies regarding ecological security alarm and ecological compensation.