Water-level-fluctuating Zone (WLFZ), is formed due to periodical or long-term water level fluctuation of rivers, lakes and reservoir, belonging to a seasonal wetland. The vegetation in the WLFZ plays a crucial role in keeping dynamic balances of terrestrial-aquatic ecosystems, biodiversity, ecological security as well as ecological services. The investigation of plant compositions, flora characteristics and community distribution characteristics resulted from vegetation were performed in present research. Results showed that a total of 115 vascular plant species belonging to 40 families and 101 genera were found in the WLFZ of the Songtao Reservoir, Hainan. In addition, 4 fern species belonging to 4 families and 4 genera were found among them. The typical tropical characters of these plant species were found via flora analyses. A large percentage of the exotic invasive species and amphibious plants with flooding tolerances and drought tolerances were found. There were many herbs and shrubs in plant communities, whereas a few arbor species with annual seedlings existed. Many Panicum repens dominant compound communities were distributed in the WLFZ. In addition, a few dominant communities, such as Wedelia trilobata, Mimosa sepiaria, Crotalaria pallida, Melochia corchorifolia, Praxelis clematidea, and Panicum repens, were found in some plots. Significant differences in community distributions among altitudes occurred. Along with elevation reduction,the species diversity decreased significantly. The results of this study may provide scientific guidance for the revegetation activities in the WLFZ of the Songtao Reservoir.