Ruditapes philippinarum, which is naturally distributed along the coast of the Pacific and India Oceans, is one of the most popular shellfish cultured in China and many parts of the world. China is the world’s largest producer of Ruditapes philippinarum. Some inappropriate ways of aquaculture, however, have resulted in the worseness of environment, which would restrict and endanger the development of aquaculture. The study of carrying capacity may resolve the problem of ecosystem by overstocking, so the study on carrying capacity of cultured tidal shellfish is very necessary. The carrying capacity for shellfish Ruditapes philippinarum that cultured in the Rushan Bay was estimated by calculating the demand for and the supply of organic carbon produced by primary production. Ingestion rate of filter-ingestion animals and other field data were used for model validation. The results obtained showed that the highest carrying capacity of the bay for the Ruditapes philippinarum occurred in October and the lowest in August in tidal cultured areas among different shell length. The average carrying capacity of the bay for the Ruditapes philippinarum with the shell length of 1.5-2.5cm was 2692ind/m2 and still in suitable opportunity, the shell length of 2.5-3.5cm was 1157 ind/m2 and near the actual culture density, and the shell length above 3.5cm was 2692 ind/m2 and over the best culture density.