Abstract: To explore the structural characteristics and the influencing factors of the phytoplankton community in Dongting Lake, an investigation  was carried out in different parts of the Lake during three hydrological periods in 2023.The results showed that a total of 44 genera belonging to 6 phyla of phytoplankton were identified in the Lake, which included 16 genera of Chlorophyta, 12 of Bacillariophyta, and 10 of Cyanophyta.The average density of phytoplankton was 83.69×104 cells/L.Bacillariophyta was identified as the most abundant one, followed by Pyrrophyta and Cyanophyta, which accounted for 62.0%, 13.1%, and 10.1% respectively.In terms of the hydrological period distribution, the average density of phytoplankton followed the order of the wet season > the normal season > the dry season.Spatially, the density was in the order of West Dongting Lake > South Dongting Lake > East Dongting Lake, with Bacillariophyta being the dominant group.The Shannon-Wiener diversity index of Dongting Lake ranged from 2.76 to 3.17.East Dongting Lake was rated as excellent, while West and South Dongting Lakes were in a good state.The comprehensive trophic state index of the whole lake was 46.7, indicating a mesotrophic level.The results of the redundancy analysis showed that the main factors affecting the distribution of phytoplankton were water temperature and dissolved oxygen.This study reflected the status of the aquatic ecological environment in Dongting Lake and provided data support for the ecological restoration, protection, and management of the Lake.