Abstract: In order to understand the characteristics of phytoplankton community structure of Feijing Reservoir, the phytoplankton samples were collected every month from June 2019 to May 2020, the annual variation characteristics, dominance, diversity and evenness indices of phytoplankton were analyzed by species identification and density statistics. The results showed that a total of 40 genera of phytoplankton identified, belonging to 7 Phyla in the water samples from Feijing reservoir, Chlorophyta was the dominant Phyla, the highest in genera, and followed by the Phyla of Bacillariophyta and Cyanophyta. Density of the phytoplankton varied in the range from 269 × 10⁴ to 1980 × 10⁴ Cells/L(816. 93 × 10⁴ Cells/L in average). The dominant genera were 20, Merismopediawas the dominant genera in September, while in the rest of the months Cyclotella was dominant genera. The indices of Shannon-Wiener and Pielou evenness ranged from 1.42 to 3.17(2. 45 in average) and from 0.37 to 0.75(0.59 in average). According to Shannon-Wiener Diversity and Pielou evenness and cell density index to assess the water quality of Feijing Reservoir, the results indicated that the water quality was slightly polluted and oligo-mesotrophic.