In recent years, the ecological environment and ecological functions of natural waters, especially reservoirs, have generally shown a degradation trend under the influence of human activities such as watershed development and pollution.The Zhanghe Reservoir is the largest independently managed reservoir in Hubei Province and a typical nutrient-poor reservoir.The phytoplankton community and water environment charac-teristics were investigated and analyzed at 21 sampling sites for four seasons from January to October 2022 to in-vestigate the community composition, distribution patterns and drivers of phytoplankton in the Zhanghe Reser-voir.A total of 223 species in 100 genera from eight phyla were identified, of which the most abundant were Chlorophyta, followed by Bacillariophyta and Cyanophyta.The dominant phytoplankton species were Cyclo-tella sp.,Lyngbya limnetica, Peridinium cinctum, Dinobryon divergems, and Scenedesmus bijuga.The phy-toplankton cell abundance varied from 3.62×106 to 4.16×107 cells/L.Temporally,the abundance was signifi-cantly higher in summer and autumn than in winter and spring, except for summer when the Cyanophyta was predominant, the Bacillariophyta was predominant in all other seasons.The Shannon-Wiener diversity index, the Pielou evenness index, and the Margalef abundance index all indicated that the Zhanghe reservoir is in a lightly polluted to moderately polluted state.Redundancy analysis (RDA) showed that water temperature, transparency, COD, DO, TN, and TP were the main environmental factors affecting the distribution of the phytoplankton community.The results of this study will help provide basic information on water resource use and water environmental protection in the Zhanghe reservoir.