Southern Ocean have uptaken ~40% of global anthropogenic CO₂ emissions, with 10% of this uptake driven by biological pump. The efficiency of biological pump is decided by both biomass and composition of primary producers, and the global elemental cycling and stoichiometry is also driven by this. Iron has been recognized as the mostly crucial limiting nutrients to primary production in the Southern Ocean. Other trace metals, such as zinc, cobalt and manganese, are also found to limit the growth of phytoplankton in the Southern Ocean. Therefore, it is important to understand the relationship between phytoplankton and environmental factors. In this study, phytoplankton composition, Chla, POC and environmental factors such as S, T, mixed layer depth, macronutrients (N, P, and Si) and trace metals (Fe, Co, Ni, Cu, Zn, Cd, and Pb) were obtained in the Ross Sea and Amundsen Sea in January 2019. Redundancy analysis of environmental factors and phytoplankton composition showed that salinity was the main influencing factor and was negatively and positively correlated with haptophytes and diatoms, respectively; manganese, nickel, copper, zinc and silicon were negatively correlated with haptophytes; and cadmium, manganese, phosphorus and silicon were negatively correlated with diatoms. Meanwhile, based on the specificity of seasonal changes in the mixed layer of the Southern Ocean, this study used the difference in nutrient concentrations between the mixed layer and 300 m water depth in summer as the phytoplankton consumption, calculated the phytoplankton uptake elemental stoichiometry ratio, and explored the relationship between uptake ratio and phytoplankton composition. The results showed that N/P, P/Fe and P/Mn decreased with increasing diatom abundance. This study offer an insight view of the interaction between trace metals and phytoplankton composition, and its potential role in influencing ecological function and biological sustainability in the Southern Ocean.