Abstract: Abstract：In order to understand assemblage structure characteristics of hygrophytes and their driving factors in the Yangtze mainstem, we carried out field investigations of hygrophytes in five sand bars in Yichang-Jianli section during March-May 2018. A total of 88 species of hygrophytes, belonging to 26 families, 73 genera were collected. Among them, Compositae, Gramineae, Polygonaceae were dominant，Cynodon dactylon、Carex leiorhyncha、Hemarthria altissima、Phalaris arundinacea were the predominant species. The average species number in plots was 6, the average density was 89 ind/m² and average biomass (above ground part, dry mass) 55.8 g/m². Assemblage structure characteristics of hygrophytes varied in space and time. Plot species number, density and biomass in the Zhicheng section were the largest, while those in Jingzhou section were the smallest. Density of hygrophytes decreased from March to May, while biomass increased. Ten dominant assemblages were identified including Carex leiorhyncha, Cynodon dactylon, Hemarthria altissima-Aster tataricus and the others. Canonical correspondence analysis indicated hygrophytic plant assemblages were mainly affected by clay proportion (Clay), elevation above water (ELEV), soil moisture (SM)and total organic matter content in soil (TOM), and the most important one was Clay. Moreover, plot total biomass changed with ELEV, SM and TOM in a similar way, i.e. it increased first and then decreased along these factors. The relationship between plot biomass and Clay was insignificant. We concluded that hygrophytic assemblages in sand bars were driven by hydrological regimes under which substrate, soil moisture and nutrients acted together to shape the assemblages.