Vegetation within riparian and floodplain undergoes significant alterations driven by climatic factors and human interventions, particularly influenced by cascade hydropower development. This study investigated the dynamics of the Normalized Difference Vegetation Index (NDVI) in riparian and representative floodplains vegetation under cascade hydropower development in the middle reach of Hanjiang River by using Landsat imagery and hydroclimatic station data. The vegetation NDVI of the riparian increased significantly (p < 0.01) during the growing season, and the vegetation NDVI of the riparian and typical floodplains also increased after the hydropower developments. In terms of the key driving factors, the increased annual water level may explain the reduction in most floodplains. Increasing temperature, especially in March, can promote vegetation growth of riparian and typical floodplains. The development of cascade hydropower may result in different contributions of climate and hydrology to vegetation at different periods, and it was found that the climate is the major contributor to the changes in the vegetation NDVI after the construction of the dam. This research will help clarify the impact of cascade hydropower development on vegetation in riparian and floodplain ecosystems. It also provides a scientific basis for vegetation protection and environmental restoration in the basin.