Abstract: In order to avoid the discharge of nitrite into the receiving water body,the feasibility of using the oxidation reduction potential (ORP) as control parameters for nitrite accumulation in SBR denitrification for the treatment of leachate via anoxic/anaerobic UASB,was investigated. Experimental results show that under the four different initial NO₃^- -N concentration used, nitrite accumulation is observed obviously in SBR denitrification. It also concludes that the nitrite accumulation rate is 0. 117,0. 136,0. 235 and 0. 068 /d, respectively. In addition,two break points of nitrate and nitrite on ORP profile indicate that the nitrate reduction reaction and nitrite reduction reaction are completed,respectively. For the denitrification,in which nitrite accumulates obviously,nitrate concentration is used as the sole parameter of the denitrification rate (r_DN) is not accurate,and the total oxidized nitrogen (NO₃^- -N + NO₂^- -N) should be used,or named as nominal r_DN. Furthermore,it concludes that nitrite accumulation is observed that at five different C/N ratios conditions,the accumulation of nitrite caused by nitrite reduction rate is slower than nitrate reduction rate,and for the nitrite peak value,it should be a rate of a balanced point according to the Monod kinetics equation analysis. The dosages of carbon source is sufficient for the conversion of NO₃^- -N → NO₂^- -N,however it is deficient for transformation of NO _x^- -N→N₂,when n(C) /n(N) was 2. 25∶ 1,3. 75∶ 1,respectively.