Abstract: To address the problem of insufficient carbon source in the treatment of aquaculture wastewater by denitrification, this study tested the effects of six carbon sources and different C/N ratio, using the removal rate of ammonium nitrogen and accumulation rate of nitrite as indicators. The results showed that carbon sources and C/N ratio did not significantly impact the removal rate of ammonium nitrogen, which was up to 98% in the treatment groups, significantly higher than that in the control group (p<0.05). When glucose and glycerol were used as the carbon sources, there was clear nitrite accumulation. When alcohols was used as the carbon source, the accumulation of nitrite was almost zero, whereas the removal rate of nitrate was up to 90%, significantly higher than that in the control group (59%). When ethanol was used as the carbon source and C/N ratio was 3.0, the removal rate of total nitrogen, ammonia nitrogen and nitrate were especially high, up to 93.28%, 98.90% and 91.82%, respectively. Although the extra carbon could substantially increase the concentration of CODMn, but it maybe rapidly degraded by denitrifing bacteria within a short time. In addition, the extra carbon could improve the stability of pH value of aquaculture wastewater to be between 7.2～7.8. The results of the present study suggest that the extra carbon source could significantly improve water quality and biological nitrogen removal efficiency during wastewater purification process in recirculating aquaculture systems.