In order to verify the effectiveness of a self-designed recirculating water treatment system, it was tested in an indoor Grass Goldfish breeding experiment for 3 months. The results showed that the system maintained water turbidity in a low level of 1.0-4.0 NTU. It efficiently degraded aqueous ammonia nitrogen and nitrite nitrogen(the degradation rate of 87.6% and 74.3%, respectively), and kept the dissolved oxygen in aquaculture water at a high level of 4.39-5.92 mg·L-1; therefore, the total number of bact...