Abstract: Based on the monitoring data of Lianshi Lake from May to September 2019,this paper analyzed the water quality, phytoplankton community structure and their relationship.As a result, the concentration of nitrogen and phosphorus in Lianshi Lake was high, and it is a slightly eutrophic water body. 65 phytoplankton species from 7 phyla were identified. Chlorophyta and bacillariophyta were the dominant species, and the average cell density of Lianshi Lake was 1.814 million cells / L. The dominant species were Chlorella sp., microcycline sp., Synechocystis sp., and Scenedesmus sp., which were mesotrophic and eutrophic water indicator species. Correlation analysis and redundancy analysis showed that nitrogen, phosphorus, permanganate index and water temperature in Lianshi Lake have the greatest impact on phytoplankton cell density and community structure.