Abstract: Measuring photosynthesis rate accurately is very important in photosynthesis studies.However it is difficult to use the common measuring methods developed in land plant studies for the measurement of photosynthesis of submerged macrophytes because of their special habitat.In this paper,the characteristics of dissolved inorganic carbon is described in detail before the introduction of the principles of pH-stat and pH-drift-the electrochemical methods measuring photosynthesis of submerged aquatic macrophytes.The changes of inorganic carbon in water solutions of the two methods can be easily calculated by Gran-titration.