In this paper, the efficiencies of dif ferent culture systems in Sishiliwan Bay, Yantai, China, were comparat ively sem-i in situ studied from April 5, 1998 to June 23, 1998. In the experiment , one control and nine culture systems, established ( 5 m @ 2 m @ 1 m in volume) near the bay, in which Chlamys farreri , Laminaria japonica , Apostichopus japonicus w ith dif ferent densities were stocked. Water exchanging quantity was 100% per day in each system. The results show that the productivities of C . f arreri in monoculture system and in polyculture system of shellf ish, seaweed and sea cucumber are 0. 56g / m2#d and 0. 78g/ m2#d respectively , and that of A . japonicus in polyculture system is 74. 7 g/ m2. The growth rate of C. farreri in monoculture system was slower than that in two kinds of polyculture systems. The eff iciency of shellfish, seaweed and sea cucumber polyculture system is better than that of shellf ish monoculture and shellf ish and seaweed polyculture systems. The optimal scallop stocking densities in monoculture system, and polyculture system of shellfish, seaweed and sea cucumber are 21. 0 and 23. 0 ind/ m 2 respectively , and the optimal densities for kelp in polyculture system of shellfish and seaweed, and in the mixed system of shellfish, seaweed, and sea cucumber are 0. 68 ind/ m 2 and 0. 71 ind/ m 2 respectively, and that of sea cucumber in polyculture system of shellfish, seaweed and sea cucumber is 2. 0 ind/ m2.