The Gracilaria circulating aquaculture was applied in three different densities of shrimp culture, 15, 30 and 45 individuals/m2, respectively to control water quality of Penaeus monodon pond to enhance shrimp culture. The density of Gracilaria was 2.5 kg/m2. After 120 days of culture, the means of body weight in the three densities of 15, 30 and 45 individuals/m2, were 16.23, 14.29 and 12.6 g, respectively. And their survival rates were 74.24, 67.5 and 52.42%, in turn. The total survival rate was 64.72%. The index appears the 30 individuals/m2 of shrimp culture density was to the advantage of economic profit. The study also indicated that Gracilaria could purify water quality, decrease ammonia-N and nitrite-N concentrations, and enhance survival rate of shrimp. Besides, different stocking density influenced growth rate, survival rate and product of shrimp.