The feeding physiological parameters of main cultured bivalves Crassostrea gigas, Ostrea cucullata, Tegillarca granosa and Sinonovacula constricta were measured in Yueqing bay and Sanmeng bay by means of flowing natural sea water. The carbon budgets of four main bivalves were estimated according to energy balance principle. The result indicated that bivalves obtain carbon source by filtering organic grain, and then some parts were directly discharged as dejection, some parts were consumed by breathing, and a little was discharged by excretion, the remaining carbon namely the growth carbon which becomes the organism composition of the bivalves for its growth and development. In spring, the net growth rate of C. gigas, O. cucullata, T. granosa and S. constricta was 53.95% ,65.78% ,55.13% ,28.12%, and the ecological efficiency was 16.33%, 22.10%, 6.09%, 6.81% respectively. The assessment indicated that in spring of 2002, cultured bivalves in Yueqing Bay and Sanmen Bay taked POC from sea water reached as much as 44.43 t and 76.88 t per day; and consumed oxygen in sea water reached which 50.68 t and 96.93 t; excrete ammonia and nitrogen reached 4.35 t and 7.97 t. Dry weights of discharged dejection of the cultured bivalves in these two bays were even more than 370 t and 580 t.