Abstract: To estimate the carbon content of marine organisms in Zhelin Bay marine ranch of the South China Sea and determine their carbon storage, we measured the carbon content of different tissues from the marine organisms in Zhelin Bay before and after ashing by elemental analysis method. The results show that:1) Before ashing, the average carbon concentrations of meat, bones(shell) and viscera were 37.72%~47.41%, 11.23%~34.91% and 27.58%~33.95%, respectively, among which Osteichihyes, Crustacea (shrimp), Gastropoda and Bivalvia had better carbon fixation ability, but except Cephalopoda, and the other species difference was not obvious. After ashing, the average carbon contents were 1.83%~8.28%, 1.90%~12.54% and 0.62%~8.29%, respectively, and the carbon fixation ability of Gastropoda was the highest, followed by that of Bivalvia. 2) The amount of fixed carbon by organisms was about 6.728×10⁴ t in Zhelin Bay marine ranch in 2013, in which 0.155×10⁴ t carbon was removed from the sea by harvests, accounting for 2.31% of the total carbon storage, and about 0.11×10⁴ t carbon was deposited on the seabed, accounting for 1.7%. In addition, about 6.46×10⁴t carbon was stored in the sea and may re-enter the carbon cycle, accounting for 95.98%. The features of marine organism carbon sinks are different, and marine ranching can increase carbon sink effectively.