Abstract: To investigate the phytoplankton community structure and its driving factors in the east Chagannaoer Lake, samples were collected on February 10, 2023 (during the ice-covered period) and August 10, 2023 (during the non-ice-covered period). The study focused on the species composition, diversity characteristics, and driving factors of phytoplankton during both periods, and providing foundational data for the stable development of the east Chagannaoer Lake wetland ecosystem. The results showed that a total of 88 species of phytoplankton were identified, belonging to 8 phyla, 10 classes, 24 orders, 39 families, and 58 genera. During the ice-covered period, 36 species of phytoplankton were found, mainly consisting of green algae, cyanobacteria and diatoms, accounting for 85.7% of the total species. During the non-ice-covered period, the number of phytoplankton species increased to 74, with green algae, diatoms and cyanobacteria accounting for 91.9%. During the ice-covered period, Chroomonas caudata was the dominant species, while in the non-ice-covered period, Microcystis sp. dominated. Oedogonium circinatum was the dominant species in the ice during the ice-covered period, whereas in the water, Chroomonas caudata prevailed. The phytoplankton density and biomass in the non-ice-covered period were 1.90 and 10.37 times higher, respectively, than those in the ice-covered period. Moreover, the diversity, evenness, and richness of phytoplankton in the non-ice-covered period were generally higher than those in the ice-covered period. In contrast, the phytoplankton community in the water during the ice-covered period was more diverse than in the ice. The non-ice-covered period provided a more favorable environment for phytoplankton growth, whereas the ice body in the ice-covered period helped to reduce water pollutants. The total nitrogen concentration, precipitation, and ice thickness were the main factors affecting phytoplankton in the east Chagannaoer Lake during the ice-covered period, while Chlorophyll a concentration, water temperature, precipitation, and pH were the main influencing factors for the phytoplankton during the non-ice-covered period.