Abstract: In order to scientifically protect the ecological health of desert lakes, the characteristics of phytoplankton community in the Hongjiannao Lake and its response to water environment changes were studied by the index method and the correlation analysis method. The results showed that a total of 58 species of phytoplankton were identified, and the species composition was diatomic-green algae type. The main dominant species of phytoplankton were Chlorella vulgaris, Synedra acus, Synedra ulna, Cyclotella meneghiniana, Navicula viridula and Ankistrodesmus angustus, and the number of phytoplankton species was highest in autumn, followed by winter and summer, and lowest in spring. The annual cell density of phytoplankton was between 8.70×10⁶ cells/L to 133.50×10⁶ cells/L, with an average of 50.62×10⁶ cells/L, and the annual biomass was between 3.090 mg/L to 114.090 mg/L, with an average of 35.030 mg/L, and based on phytoplankton density, there were seasonal differences in density-based clustering of survey points. The mean value of Shannon-Wiener diversity index, Pielou evenness index and Margalef abundance index were 2.684, 0.817 and 1.719, respectively, indicating that the diversity of phytoplankton in autumn and winter were higher than that in summer and spring. The biodiversity index and the comprehensive trophic level index showed that the water quality was slightly eutrophicated in the Hongjiannao Lake. Redundancy analysis showed that water temperature, water deepth, dissolved oxygen concentration and total phosphorus concentration were the main environmental factors that significantly affected the seasonal dynamics of phytoplankton community, and the influencing factors were different in different seasons. The ecological replenishment and scientific management of water resources had a positive effect on the water ecological health of the Hongjiannao Lake.