The biodiversity and biomass of floodplain vegetation are important indexes to explain the ecosystem of wetlands and key methods to probe the response mechanism to water level change. Poyang Lake is the largest fresh-water lake in China and one of the most important wetlands globally. In a field survey, 3s technology and DEM data were used to analyze the variation in plant species diversity and biomass along the elevational gradient in Poyang Lake wetlands with α and β biodiversity indexes. The results showed that there was a complex gradient of both biodiversity and biomass characteristics for the floodplain vegetation (P < 0.001). The index of biodiversity is highest at 14-15 m in Banghu Lake and Sizhoutou floodplain; the index of biodiversity is the highest at 15-16 m in Zhanbeihu Lake and Beishenhu Lake floodplain, but the index of biodiversity is not obvious in Changhuchi Lake floodplain. The correlation between biodiversity/biomass and elevation was nonlinear, and with increasing elevation, the biomass initially increased to a peak value and then decreased. The maximum volume of biomass measured in the fronted floodplain and the shallow lakes were different (P < 0.05); the maximum volume of biomass was located at an elevation of 14-15 m in fronted marshland, and at an elevation of 15-16 m in the shallow lakes.