Abstract: In order to explore the community structure and biodiversity characteristics of phytoplankton in Yichang reach of Yangtze River and its relationship with environmental factors, we monthly monitored the phytoplankton community in Yichang reach of Yangtze River in 2015. The results identified phytoplankton of 41 genera in 8 phyla in the reach, of which 7 genera of Cyanophyta, 1 genus of Cryptophyta , 2 genera of Pyrrophyta, 1 genus of Chrysophyta, 1 genus of Xanthopyta, 14 genera of Bacillariophyta, 2 genera of Euglenopyta, 13 genera of Chlorophyta. Chlorophyta in spring, Cyanophyta and Bacillariophyta in summer, Bacillariophyta in autumn, Chlorophyta and Bacillariophyta in winter were the dominant algae species. The Shannon-Weaver diversity indexes and Pielou evenness indexes showed that Yichang reach were moderately and lightly polluted. The results were basically consistent with the results of the comprehensively evaluated nutrition status of the water body. The correlation analysis between environmental factors showed that, under the influence of the Three Gorges reservoir operation, the change of hydrodynamic condition is the main influential factors to the community structure of phytoplankton and water quality in Yichang reach.