Hygrophilous vegetation plays a critical role in the processes of wetland ecosystem material circulation and energy transformation. Species diversity of hygrophilous vegetation communities can reflect the stability, as well as complexity of wetland ecosystem structure. Random subplots and sampling lines were utilized to investigate the typical hygrophilous vegetation communities in Poyang Lake wetland. Results showed that the average important values of dominant species of studied typical hygrophilous vegetation communities were above 0.5, which indicated their dominant status. Compared to those in spring, the diversity of Carex argi community, Polygonum hydropiper community, Zizania latifolia community, Typha angustifolia community and Miscanthus sacchariflor community declined in autumn. However, the biodiversity of Phragmites communis and Carex cinerascens community ascended in autumn, this is because that the dominance of the dominant species was weaken by delayed recession of water level, while frequently switching between grass beach and water brought substantial nutrients in autumn. Because of different growth mechanisms and niche overlapping, the diversity of Phragmites communis community and Miscanthus sacchariflor community had a reciprocal relationship along the seasons. At last, insignificant correlation was found between plant biomass and biodiversity indices.