Abstract: The effects of CO2 concentration on the growth and photosynthesis of Dicrateria zhang, jiangensis and Dunaliella sp, in 100 liter air lift photobioreactors were investigated. The results showed that biomass of both algae significantly increased in high CO2 concentration (above 700μL ? L^-1) compared to low CO2 concentration (350μL?L^-1) ,and the culture periods were shorter, However, no significant difference as observed in growth rate when the alga cultured in CO2 concentration of 700μL? L^-1 and 1000μL? L^-1, respectively. These for the maximum photosynthetic rate(Pm) and saturating irradiance level(Ik) of the two species remarkably raised with the elevated CO2 concentration, so was the initial slope(α)of Dunaliella sp.