The structure and dynamic characteristics of wetland vegetation communities are important indicators reflecting the health of the wetland ecosystem, which are essential for predicting the direction of development and ecological restoration of the wetland ecosystem. Based on the 30-m and 8-day resolution NDVI dataset obtained by fusing Landsat and MODIS data, we adopted a phenology-based decision tree approach to map the spatial distribution patterns of different vegetation communities in the floodplain wetland of Lake Poyang from 2000 to 2020, and analysed the spatiotemporal dynamics and transformation processes of different vegetation communities. The results indicated that the spatio-temporal adaptive fusion model for NDVI products (STAFFN) could provide a powerful database for fine classification of wetland vegetation in Lake Poyang. The study area was classified into eight landscapes using a phenology-based decision tree approach: water, mudflat, floating aquatic macrophyte community, Polygonum hydropiper-Phalaris arundinacea community, Carex community, Phragmites australis-Triarrhena lutarioriparia community, Artemisia selengensis community and forest. The overall classification accuracy was 89.36%. Within the whole lake, the total vegetation cover fluctuated, but showed a significant increasing trend during the observation period. Among the different vegetation communities, the Polygonum hydropiper-Phalaris arundinacea community showed the most significant increase, while the Carex community, which is the most widespread, first increased and then decreased slightly, and the Phragmites australis-Triarrhena lutarioriparia community, which is the subdominant species, fluctuated between 300 and 500 km². Comparison of the sub-lake regions showed that the trend in the Carex community was relatively clear in the northern and eastern regions. There were spatial differences in the distribution of the subdominant species. The northern and eastern regions were dominated by the Polygonum hydropiper-Phalaris arundinacea community, while the southern region was dominated by the Phragmites australis-Triarrhena lutarioriparia community. In addition, the landscape evolution trend of Poyang Lake wetland during 2000-2020 showed a transitional characteristic from water → mudflat → lower flat vegetation (Carex community and Polygonum hydropiper-Phalaris arundinacea community) to mutual transformation of Carex community and Phragmites australis-Triarrhena lutarioriparia community. The overall situation was that the vegetation (e.g. Phragmites australis, Triarrhena lutarioriparia, etc.) on the higher level expanded towards the lower level and the Carex, Phalaris arundinacea and Polygonum hydropiper, etc. on the lower level expanded towards the centre of the lake.