Phytoplankton play a key role in maintaining the stability and function of ecosystems. However, there is still limited research on the structure of phytoplankton communities in lake ice during the ice-covered period and their relationship with environmental factors. 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 Juye Lake, Wuliangsuhai, Hasuhai, and Chagannaoer. The results showed that: (1) A total of 132 species of phytoplankton were identified in the ice layers of Wuliangsuhai, Dong Juye Lake, Chagannaoer, and Hasuhai. In Dong Juye Lake, 26 species of phytoplankton were identified, with Chlorella sp. as the dominant species; in Wuliangsuhai, 80 species were identified, with Zygnema sp. as the dominant species; in Hasuhai, 54 species were identified, with Microcystis sp. as the dominant species; and in Chagannaoer, 34 species were identified, with Anabaena as the dominant species. (2) The ecosystem in Dong Juye Lake ice was relatively simple with low biodiversity; the ecosystem in Wuliangsuhai ice was rich with high biodiversity; the biodiversity in Hasuhai and Chagannaoer ice was at an intermediate level. The similarity of algae species between different lakes showed significant differences. The highest similarity was found between Wuliangsuhai and Hasuhai, while the greatest difference was observed between Dong Juye Lake and Wuliangsuhai, with Chagannaoer showing some uniqueness. The density of phytoplankton in lake ice showed a significant positive correlation with total nitrogen, ice temperature, and salinity, and a significant negative correlation with pH and chlorophyll a concentration.