CO2 emissions have serious impact on the world economy, especially at high-concentration. Green algae are known to have a tolerance to high CO2 level. In this paper, the rate of CO2 fixation using Chlorella Pyrenoidosa was analyzed in different environments. 1) Chlorella Pyrenoidosa fixed CO2 slowly in air, while this alga could rapidly grow in high-concentration CO2 until CO2 level was beyond 10%. At 25% CO2, the rate of CO2 fixation was lower than that at 10% CO2, but still 1.18 times as higher as in air. 2) At lower initial inoculation density of Chlorella Pyrenoidosa, its growth rate was relatively high but the rate of CO2 fixation was low. When initial inoculation density beyond 0.187×108cells/ml, the average rate of CO2 fixation was ranged from 2.786 gCO2/L·d to 2.847 gCO2/L·d. 3) During the five days, the average rate of CO2 fixation was 3.044 gCO2/L·d in NaNO3 resource. When NH4Cl or NaNO2 is regarded as N resource, the rate of CO2 fixation was almost neglectable.