Vegetation is a crucial component of riverine floodplain systems, serving vital ecological and environmental functions while acting as a primary indicator of external disturbances. Dam operations alter the succession trajectories of downstream floodplain vegetation by regulating hydrogeomorphic processes. However, current global-scale land-use datasets and vegetation maps are limited by poor spatiotemporal resolution and coarse classification granularity. Focusing on the floodplains along the Middle Yangtze River (MYR), this study develops a vegetation identification method that integrates high-resolution and long-term time-series remote sensing imagery. We reconstructed the spatiotemporal distribution patterns of floodplain vegetation community over the past 40 years and revealed the succession dynamics before and after the operation of the Three Gorges Project (TGP). The main findings are as follows: (1) Over the past 40 years, the proportion of bare floodplains in the MYR decreased by 17.3%, while vegetation-covered floodplains increased by 13.0%; (2) The expansion of floodplain vegetation primarily occurred post-TGP operation but prior to the operation of the upstream cascade reservoirs. During this period, driven by reduced inundation frequencies, the vegetation cover in the MYR experienced a net expansion of approximately 91.0 km²; (3) Following the TGP operation, progressive succession from early-stage to late-stage communities increased significantly but subsequently declined. Conversely, retrogressive succession has continuously increased since the TGP operation due to persistent bank collapse; (4) The direction of community succession is primarily driven by changes in inundation frequency. Decreased inundation frequency, caused by flattened flow regimes and floodplain aggradation, drives progressive succession; whereas increased inundation frequency resulting from bank collapse drives retrogressive succession. These findings provide a robust scientific basis for the conservation and ecological restoration of floodplain ecosystems in the MYR.