Abstract: The effects of long-term elevated CO2 on functions of PSⅡ in soybean leaves were studied. The results showed that the potential activity and efficiency of primary conversion of light energy of PSⅡ , quantum of PSⅡ electron transport were stimulated, photochemical quenching coefficient was increased and non-photochemical quenching coefficient was decreased under elevated CO2. The improvement of PSⅡ functions could be one of important factors which result in increases of the photosynthetic rate and yield of soybean under elevated CO2.