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Vegetation, as a comprehensive ecological indicator of environmental change, plays an essential role in terrestrial ecosystems. Dramatic climate change and increasing anthropogenic disturbances have led to a profound change in vegetation cover. This study employed Moderate Resolution Imaging Spectroradiometer (MODIS) and other relevant data in Southwest China mountains, using Chongqing as a case study, to explore the variation in Normalized Difference Vegetation Index (NDVI) and its spatial differentiation mechanisms, quantify the relative contributions of climate change and human activities to these variations, and assess the effects of ecological policies, including afforestation, mountain closure forestry and natural forest conservation, and agricultural improvement. Results showed that the spatial distribution of annual NDVI, on average, varied 0.109 to 0.929, with the rate varying from −0.033 to 0.017 yr−1. NDVI was improved in 83.4% areas of Chongqing, and human activities contributed 69.1% of revegetation, whereas climate contributed 30.9%. On the other hand, human activities and climate change contributed 76.3% and 23.7% to vegetation degradation in 17.6% areas, respectively. Moreover, the explanatory power of anthropogenic factors on spatial differentiation of NDVI were stronger than that of climatic factors, and land use type was the dominant factor. The cumulative afforestation area, effective irrigation rate, fertilizer application, and total agricultural machinery power of the whole city was extremely significantly correlated with NDVI (p < 0.01), and the vegetation cover fluctuation in the region affected by natural forest protection and mountain closure forestry project was much more stable than that in non-protected areas, which to a certain extent reflected the effective implementation of local ecological protection, agricultural improvement, and other related policies. [ABSTRACT FROM AUTHOR]