Global warming is mainly caused by the excess carbon dioxide (CO2 ) in air. As the largest store of CO2 on the earth, ocean plays an extremely important role for regulating the CO2 concentration in the atmosphere. Getting the information on the spatial and temporal distribution of CO2 in seawater timely is very important for studying the marine carbon cycle, the marine ecology and the change in global climate. Therefore, it is important and necessary to develop a high-precision and low-power detecting instrument for in situ measurement of CO2 in the sea.