Abstract: Phytoplankton community characteristics are a basic information of aquatic ecosystems. The Three Gorges Reservoir (TGR) is an important area of environmental protection in the Yangtze River Economic Zone, however the basic information for the phytoplankton community characteristics in the whole reservoir and the influencing factors are rarely reported. To fill this gap, the field survey, including 17 transects (51 sites) in 484km main channels of TGR and 22 tributary bays (122 sites), was carried out in April 2015 to investigate the fundamental information of the water environment and phytoplankton community. A total of 61 species, belonging to 39 genera in 7 phyla were identified. Specifically, for the richness, Chlorophyta (26 species) is the most important component, accounting for 42.62% of the total species number; followed by Bacillariophyta (16 species) for 26.23%, and Pyrrophyta (7 species) for 11.48%. For abundance, Bacillariophyta dominated in all phyla, accounting for 34.26% of the total abundance; followed by Cryptophyta for 23.72%, and Cyanophyta for 20.96%. For biomass, Pyrrophyta is the most important component, accounting for 44.18% of the total biomass; followed by Cryptophyta for 29.92%, and Bacillariophyta for 14.32%. The abundance and biomass of phytoplankton for each site in the Three Gorges Reservoir ranged from 2.22×104-5.12×107 cells/L and 0.001 8-120.99 mg/L, respectively. In addition, we found that i) both the values of abundance and biomass were increasing from the dam of TGR to the upper reache of the Yangtze River ii) the Shannon-Wiener diversity index of phytoplankton in the tributary bay was significantly higher than that in the main channel (Mann-Whitney U test, P < 0.001). Further, redundancy analysis showed that water temperature and dissolve silicate were the main environmental factors affecting the phytoplankton community in the main channel (P < 0.001); while, nitrate and water temperature  were the main factors determining phytoplankton community in the tributary bays (P = 0.002). The results of this study give us a comprehensive understanding of the community structure of spring phytoplankton and the influencing factors in the TGR. Meanwhile, it also has some values for ecological protection and water resources management for the TGR.