Abstract: We compared the utilization of Ca2+ and HCO3- in typical karst water by exogenous chlorella and native chlorella in a closed system. Analyzed the relationship between chlorella cell numbers and the utilization rate of Ca2+ and HCO3- and the variation of pH value. The results showed that the native algae had higher ability in utilizing Ca2+ and HCO3- than exogenous chlorella, while exogenous chlorella had higher Ca2+ utilization amount than native algae. The utilization amounts of HCO3- of them were the same. In addition, exogenous chlorella can form CaCO3 sediment, but native can not. The variation of pH value in the closed system revealed that both of the two algae firstly utilized the dissolved carbon dioxide as photosynthesis carbon source, and then made use of HCO3-. Exogenous chlorella absorbed 29.648% HCO3- in the karst water, native algae utilized 40.625% HCO3-. As the primary producer in the food chain, the two kinds of aquatic algae transformed HCO3- and took it into the ecological system.