Abstract: Hybrid biological reactor (HBR) was operated in a sequence,which available capacity was 12 L (filled media 30 %,υ/υ),simultaneous nitrification and denitrifieation (SND) via nitrite were achieved in a single reactor by controllingρ(DO) (at the end of the aeration period) concentration.The result showed that:with the increase ofρ(DO),the rate of the ρ(NO₂^- -N)/ρ(NO_x^- -N) and the removal efficiency of TN were decreased.When theρ(DO)>4 mg/L the rate of theρ(NO₂^- -N)/ρ(NO_x^- -N) and the removal effi- ciency ofρ(TN) were less than 50%.The rate of theρ(NO₂^- -N)/ρ(NO_x^- -N) above 85%,the removal efficiency ofρ(NH₄⁺ -N) was over 98%,and the removal efficiency ofρ(TN) was about 7596,by control- lingρ(DO) around 2 mg/L,and temperature at (28±1)℃.In conclusion,stable nitrogen removal from wastewater by SND via nitrite at normal temperature could be achieved so long asρ(DO) was controlled at 2 mg/L.