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 Dong Juyehai, Wuliangsuhai, Hasuhai, and Chagannaoer. The results showed: (1) A total of 132 species of phytoplankton were identified in the ice layers of Wuliangsuhai, Dong Juyehai, Chagannaoer, and 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 Dong Juyehai ice, 26 species of phytoplankton were identified, with Chlorella sp. as the dominant species; in Wuliangsuhai ice, 80 species were identified, with Limnothrix sp. as the dominant species; in Hasuhai ice, 54 species were identified, with Microcystis sp. as the dominant species; and in Chagannaoer ice, 34 species were identified, with Ulothrix zonata as the dominant species. (3) The ecosystem in the ice of Dong Juye Lake is relatively simple, with low phytoplankton diversity; the phytoplankton diversity in the ice of Wuliangsuhai Lake is higher; the phytoplankton diversity in the ice of Hasu Lake and Chagannaoer Lake is at a moderate level. The similarity of algae among different lakes varies significantly, with the highest similarity between Wuliangsuhai Lake and Hasu Lake, the largest difference between Dong Juye Lake and Wuliangsuhai Lake, and Chagannaoer Lake 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.