Phytoplankton is a major participant in the material and energy cycles of lake ecosystems,and the information of its community structure is of great significance in coping with and regulating lake ecosystems.In this study,the community characteristics of eukaryotic phytoplankton in the western Chaohu Lake in winter and summer were obtained via high-throughput sequencing.A total of 7 phyla and 71 genera of eukaryotic phytoplankton were detected during the survey,including 7 phyla and 59 genera in summer and 5 phyla and 27 genera in winter,dominated by Chlorophyta and Bacillariophyta,and the dominant genera varied greatly in winter compared with those in summer.The mean values of Shannon-Wiener index in summer and winter were 1.83 and 1.88 respectively,and the Pielou index were averaged 0.75 and 0.83 for summer and winter respectively.The results of water quality analysis indicated that TN and TP were relatively high in the western Chaohu Lake during the study period,and the physicochemical factors of the water body varied significantly between summer and winter (P≤0.05).Redundancy analysis showed that the eukaryotic phytoplankton community can be roughly explained by PO₄^--P,TN,TP and NH₄⁺-N,especially the PO₄^--P (P≤0.05).Mantel correlation analysis showed a close correlation between eukaryotic phytoplankton abundance and WT,DO,pH,NH₄⁺-N,TN and Chl.a.Variance partitioning analysis showed that seasonal factors explained most of the eukaryotic phytoplankton community dynamics.