Phytoplankton play a key role in maintaining ecosystem stability and function. However, research on the community structure of phytoplankton in lake ice during the ice-covered period and its relationship with environmental factors remains limited. To reveal the characteristics of phytoplankton communities in lake ice and their influencing factors, a sampling survey was conducted in February 2023 on the phytoplankton and physicochemical indicators in the ice of Lake Dongjuyanhai, Wuliangsuhai, Hasuhai, and Chagannaoer. The results showed: (1) A total of 132 species of phytoplankton were identified in the ice layers of Lake Wuliangsuhai, Lake Dongjuyanhai, Lake Chagannaoer, and Lake Hasuhai, with Cyanophyta dominating in abundance, accounting for 50.01%. In terms of species number, Chlorophyta and Bacillariophyta accounted for 34.85% and 33.33%, respectively. (2) In Lake Dongjuyanhai ice, 26 species of phytoplankton were identified, with Chlorella sp. as the dominant species; in Lake Wuliangsuhai ice, 80 species were identified, withLimnothrix sp. as the dominant species; in Lake Hasuhai ice, 54 species were identified, withMicrocystis sp. as the dominant species; and in Lake Chagannaoer ice, 34 species were identified, withUlothrix zonataas the dominant species. (3) The ecosystem in the ice of Lake Dongjuyanhai is relatively simple, with low phytoplankton diversity; the phytoplankton diversity in the ice of Lake Wuliangsuhai is higher; the phytoplankton diversity in the ice of Lake Hasuhai and Lake Chagannaoer is at a moderate level. The similarity of algae among different lakes varies significantly, with the highest similarity between Lake Wuliangsuhai and Lake Hasuhai, the largest difference between Lake Dongjuyanhai and Lake Wuliangsuhai, and Lake Chagannaoer exhibiting some uniqueness. (4) In the ice layers of different lakes, the survival of dominant phytoplankton species was influenced by a combination of environmental factors, including salinity, temperature, total nitrogen, and total phosphorus, with significant differences in the response of different species to these factors. Future studies should focus on the dynamic relationship between dominant phytoplankton species and environmental factors in ice layers to better guide lake ecological conservation.