Danjiangkou Reservoir is water source of Middle Route Project of the South-to-North Water Diversion (SNWD) Project, research on the dynamic changes in vegetation cover and its influencing factors is of great significance for understanding the ecological environment of the water diversion area and formulating protection measures. In this study, the normalized difference in vegetation index (NDVI) was used to analyze the dynamic changes and influencing factors of vegetation in the upstream and downstream of Danjiangkou Dam from 1982 to 2018. The results showed that the NDVI exhibited an upward trend of 0.017 year⁻¹ (P < 0.05), and that the significantly increased area was located near the valley upstream of the dam, while the significantly decreased area was mainly distributed in the basin downstream of the dam and around the central city. The comprehensive contributions of climate and human activity factors to NDVI changes were 92.03% and 7.97%, respectively. The human activities in the upstream of the dam were mainly reflected in the ecological measures such as returning farmland to forest; the human activities at the downstream of the dam were mainly reflected in urban expansion, occupation of cultivated land and forest land by construction land.