Abstract: Using sealedtop chamber of artificial environment control system, we studied the effects of elevated CO2 (850μmol/mol) on the photosynthetic characteristics, morphological traits and biomass of a dominate aquatic plant (Scirpus validus) of plateau wetland in Yunnan. The results showed that net photosynthetic rate, intercellular CO2 concentration and water use efficiency of Svalidus significantly improved. Conversely, stomatal conductance and transpiration rate decreased. Svalidus grown under elevated CO2 showed lower plant height and higher basal diameter, but the difference was not significant under two CO2 concentrations. Underground biomass and total biomass of Svalidus increased significantly compared with the control, and rootshoot ratio increased obviously as well. The more accumulation of biomass is helpful to increase the primary productivity of wetland ecosystem and the carbon input of wetland.