The paper introduced that there were 132 species of phytoplankton were identified during the survey period in TongzhangRiver district, Three Gorges Reservoir,including 23 species of Cyanophyta, 2 species of Cryptophyta, 3 species of Pyrhophyta, 55species of Bacillariophyta, 3 species of Euglenophyta and 46 species of Chlorophyta.Bacillariophyta has the most diversified spe-cies, while Pyrhophyta and Cryptophyta were the abundant ones.The dominant species were Ceratium hirundinella and Crypto-moms sp. The species and abundance of phytoplantkton varied with seasons and survey areas.Water quality assessment was calcu-laced by using the chemical and physical index, saprobic indicator and saprobic community indicator, overall evaluation result ofwater quality was V,and thep-type of moderately polluted type.