Abstract: Effects of doubled CO2 on the contents of chlorophyll and carotenoid in unit fresh weight of leaves and the fluorescence induction kinetics parameters of soybean grown under different nitrogen nutrition levels were studied in this paper. The experimental results showed that the content of chlorophyll was raised by the application of nitrogenous fertilizer and doubled CO2, respectively. However. the action of duobled CO2 can be strengthened by the application of nitrogenous fertilizer.The photosynthetic functions of soybean can be improved by doubled CO2 and the application of nitrogenous fertilizer, respectively. PSII activity and the efficiency of potential photosynthetic quantum conversion of a leaf, the proportion of PSII reaction center opened part were raised and the dissipation of non-radiation energy was reduced by doubled CO2 and the application of nitrogenous fertilizer under atmospheric CO2,respectively. Therefore, light energy captured by leaves can be fully utilized for their photosynthesis. As a result of it, the overall photochemical quantum yield of PSII was raised. The photosynthetic functions improved by doubled CO2 can be also promoted by the application of nitrogenous fertilizer. It shows that nitrogenous fertilizer should be applied when C3 plants are grown under the environment of high CO2 concentration.