Inundation dynamics of lacustrine wetlands impact the surrounding ecosystems significantly. After the operation of the Three Gorges Dam (TGD), the inundation dynamics of Lake Poyang wetland have been changed dramatically, which is triggering substantial ecological effects. The spatiotemporal evolution of the inundation dynamics of the Lake Poyang wetland in the post-TGD Era has not been systematically quantified yet, which additionally restricts the understanding of the causes and mechanisms of these ecological variations. This study measured inundation dynamics of the Lake Poyang wetland quantitatively via three variables, i.e., the start of the first inundation (SFI), the end of the last inundation (ELI), and the inundation duration (IDU) through combining hydrological data and remote sensing data. The tendency and magnitude of changes in these variables after TGD were systematically revealed at both field and regional scales. Results showed that: (1) During 2000-2020, SFI of the nearly 64% wetland was delayed and the delay rate was about 1.10 days per year. However, in the narrow channel between the lake and the Yangtze River, and the shallow depressions on the bottomland, most sites were inundated prematurely after TGD. (2) For the end of the last inundation, ELI values for nearly 72% of the wetland were significantly advanced with a rate of 1.46 days per year. In the remaining areas, such as the gate-controlled depressions, however, the ELI values were postponed due to the delayed drainage of these gates. (3) Consequently, inundation duration of the Lake Poyang wetland was notably shortened in 70% of the study area with a rate of 2.19 days per year, whereas the inundation duration of the depressions controlled by gates was prolonged in the post TGD era. Our findings quantitatively assessed changes in inundation dynamics of the Lake Poyang wetland after TGD at both field and regional scales. It revealed a great difference of inundation dynamic changes between depressions and the main lake area. This study deepens the current understanding of hydrological impacts of TGD on the Lake Poyang wetland, and provides theoretical and data basis for water resources management and ecohydrological process regulation in the study area.