Through an activated sludge SBR reactor,the authors study the influence of FA concentration and pH on the partial nitrification of low C/N nitric wastewater.It can be known that low C/N nitric wastewater can realize stable nitrite accumulation to 90%.Maintaining the pH between 6.5~8.5 is suitable for the growth of ammonium oxidation bacteria.While FA rising,the inhibition of ammonium oxidation bacteria is quick,but nitrite oxidation bacteria's is slow.By(adapting) for some time,ammonium oxidation bacteria gain the dominance,and nitrite oxidation bacteria in pessimum,which leads to the nitrite accumulation.Relatively high FA concentration is avail for the competition of ammonium oxidation bacteria.Suitable FA concentration is 7~10 mg/L.Process with long MCRT can not realize stable partial nitrification.The bacillar sludge is its typical feature.