Plant is the core component of constructed wetland. Selecting the superior varieties of wetland plants would make full use of their functions in constructed wetland, and then improve the efficiency of sewage water treatment. To investigate the growth characteristics and radial oxygen loss(ROL) from roots of wetland plants under extreme condition, 8 species of wetland plants which were cultured with synthetic water under anaerobic condition were collected for comparison. 8 wetland plants could divided into two groups, fibril-root plant(Typha orientalisl, Canna indica, Juncus effusus, Cyperus papyrus) and rhizomatic-root plant(Acorus calamus, Thalia dealbata, Arundo donax, Iris pseudacorus). The eco-physiological characteristics, such as biomass, relative growth rate(RGR) root length, root porosity, root ROL were compared. Results showed that 8 kinds of wetland plants all grown well under anaerobic conditions. Fibril-root plants had greater biomass, higher RGR and ROL than rhizomatic-root plant. Under the same illumination, Juncus effuses had the maximum ROL which reached 192.62μmol O₂/(d·g (DW_root)), while Iris pseudacorus had the minimum, which was only 68.81μmol O₂/(d·g (DW_root)). The ranking order of ROL of the 8 species wetland plants was: Juncus effuses> Cyperus papyrus> Typha orientalis> Canna indica> Acorus calamus> Thalia dealbata> Arundo donax> Iris pseudacorus. ANOVA analysis indicated that Rate of ROL was positively correlated with root porosity. The ROL was positively correlated with both of RGR and biomass,while negatively related to root/shoot ratio.