Abstract: Accumulating nitrite during denitratation could afford electron for anaerobic ammonium oxidation(ANAMMOX),using sludge fermentation liquid as carbon source to enhance nitrogen removal draw much attention in recent years. Bath experiments were conducted to investigate the effect of the ratio of soluble chemical oxygen demand and nitrate(ρ(SCOD)/ρ(NO₃^--N)) and step-feeding carbon on nitrite accumulation by using the sludge fermentation liquid as carbon source.Resultsshow that nitrite accumulation was observed at all the ρ(SCOD)/ρ(NO₃^--N),and under the ρ(SCOD)/ρ(NO₃^--N)below 4. 0,the maximum nitrite accumulation amount and nitrite accumulation rate increases with theρ(SCOD)/ρ(NO₃^--N),which reached 12. 83 mg/L and 0. 107 mg/(L·min) respectively. There was slight difference of the maximum nitrite accumulation by step-feeding carbon compared with once feeding.However,stable NAR was achieved with step-feeding. Furthermore,a positive relationship was observed between the N2 O production and ρ(SCOD)/ρ(NO₃^--N) during denitrification. This is mainly caused by the nitrite accumulation in denitrification process and the low pH of sludge fermentation liquid.Therefore,significant advantage would be obtained by step-feeding sludge fermentation liquid in establishing the denitrifying ammonium oxidation(DEAMOX) system for its stable nitrite accumulation,less inhibition on ANAMMOX of organic matter and low N2 O production.