To study the distribution of phytoplankton and evaluate water quality of Hejiang River, a branch of Xijiang River, Pearl River drainage basin, the community structure of phytoplankton was investigated and analyzed in wet and dry seasons in 2013.The results showed that a total of 130 species belonging to seven phyla of phytoplankton was identified.Including 63 species of seven phyla in wet season and 103 species of five phyla in dry season, phytoplankton community structure in Hejiang River was represented by Chlorophyta, Bacillariophyta and Cyanophyta.Chlorophyta was dominant in wet season, followed by Bacillariophyta.The mean value of phytoplankton density was 2.13×10⁶ cells/L.Bacillariophyta dominated the phytoplankton in dry season, and the mean value of phytoplankton density was 3.71×10⁶cells/L.The dominant species were Microcystis flos-aquae, Anabaena circinalis, Oscillatoria tenuis, Cryptomonas erosa, Navicula exigua, Melosira varians, Melosira granulata, Scenedesmus quadricauda, Actinastrum hantzschii, Chlamydomonas microsphaera and Chlorella valgaris.Based on RDA analysis, nitrogen and phosphorus were important environmental factors that affected the distribution of phytoplankton in Hejiang River.The river was classified as mesotrophic according to comprehensive trophic state index.