Bivalves play an important role as carbon sinks by absorbing and fixing CO₂ in seawater. This study explores the carbon sequestration capacity (CSC) of different species and sizes of bivalves by determining its carbon stocks in Yantai sea area. The results showed that the CSC of different species differed greatly, and increased significantly with individual size. The CSC of Crassostrea gigas, Ostrea plicatula, Chlamys farreri, Argopecten irradians and Mytilus galloprovincialis were 3.37~16.64g·a^-1，2.87~14.17g·a^-1，0.41~4.19g·a^-1，3.16~1.73g·a^-1and 0.21~0.38g·a^-1, respectively. The CSC of oysters was much higher than that of scallops and mussels (P<0.01), and there was no significant difference among different sites. In addition, based on the measured and the standard reference value of parameters of bivalves carbon sink evaluation, the actual amount of oyster carbon sinks in the three areas was significantly higher than the estimation based on standards (P<0.01), and the opposite was true for scallops. There was no significant difference between the actual carbon sinks ofA. irradians and M. galloprovincialis in Changdao waters and the standard estimation (P<0.01), which was related to bivalve species and individual sizes, reflecting the complexity and importance of bivalve carbon sink accounting methods.