Abstract: 76 species of phytoplankton belonging to 47 genera and 6 phyla were identified by collecting water samples from the five sampling points (Zhuan Pond Park, New Zhuan Pond Park, Mingbo Overpass, Dock, Daguan Building) along the Daguan River and through microscopic examination. Among which 36 species were from phylum Chlorophyta, 21 species were from phylum Cyanophyta. 22 species of zooplankton including Protozoan, Rotifera, Cladocera and Copepoda were identified. According to the pollution extent and the water quality criteria, it was analyzed and evaluated that the overall water quality of Daguan River was slightly to moderately polluted oligotrophic water. The water quality was significantly improved during the rainy season. But the pollution might be deteriorated during the dry season if there were no enough control measures to be taken.