Abstract: In order to discuss the effect of breeding density on juvenile Oreochromis niloticus in recirculating aquaculture system, the same batch of juvenile Oreochromis niloticus were feeding. The change of growth indicators were measured under four different groups, and the economic efficiency was calculated. Results show that the breeding density has a certain influence on the growth of juvenile Oreochromis niloticus. Along with the rising of the breeding density, the survival rate of juvenile fish and the final average weight and body length, showed a downward trend, and specific growth rate, average weight, growth efficiency, fat full growth index also showed similar rules, such as the growth indicators of the lowest density of A group was higher than the highest density of group D. High density would inhibits the growth of juvenile Oreochromis niloticus. Economic benefit analysis shows that the yields of group C was highest, which was more suitable for the breeding density.