Anoxic/Oxic Membrane Bioreactor (A/O-MBR) was used to treat domestic sewage, the effect of different sludge retention time (SRT) on nitrogen removal and the sludge properties were investigated. The results indicated that the change of NH3-N removal increased gradually with the SRT extension, then basically tends to be stable. The systematic elimination effect of TN rises with the SRT extension and then slightly tends to decrease. MLVSS/MLSS presents a gradually declining trend with the SRT extension. Sludge volume index (SVI) reduces along with the SRT extension according to the exponential decay tendency, but sludge sedimentation rate (SV30) increases progressively by two step multinomial tendency.