Since the operation of the Three Gorges Project in 2003, the hydrological regime of the Lake Dongting wetlands had undergone significant changes, subsequently affecting the distribution pattern of wetland vegetation. However, the complex relationship between the hydrological regime and vegetation distribution and the underlying mechanisms remain unclear. This study analyzed the spatial and temporal evolution of the Lake Dongting wetland vegetation pattern from 1995 to 2022 through remote sensing interpretation and field investigations. Combined with hydrological data, this paper explored the changes in inundation duration of sandbar vegetation before and after the Three Gorges Project and the driving mechanisms behind these changes. The results showed that: 1) The interannual trends of water levels in east, west, and south Lake Dongting were generally consistent. The operation of the Three Gorges Project led to a continuous decline in the annual average water level of Lake Dongting, with an average decrease of over 0.3 m and a maximum annual water level decrease exceeding 0.6 m. The duration of high water levels in west and south Lake Dongting shortened, shifting gradually toward lower water levels; 2) From 1995 to 2022, the overall trend of vegetation succession in the Lake Dongting wetlands were positive, with a continuous expansion in wetland vegetation area, specifically characterized by the encroachment of Phragmites australis communities on Carex brevicuspis, and C. brevicuspis communities on bare mudflats. 3) Changes in inundation duration before and after the operation of the Three Gorges Dam were significant in areas undergoing positive succession, from bare mudflats to C. brevicuspis and from C. brevicuspis to P. australis, whereas the changes were not significant in areas experiencing regressive succession, from C. brevicuspis to bare mudflats and from P. australis to C. brevicuspis. This suggests that reductions in inundation duration are a key driving factor promoting the positive succession of wetland vegetation in Lake Dongting.