For the treatment of municipal wastewater, the effects of the reversed A2/O-MBR system on COD, NH4+ -N, TN, TP, SS and transmembrane pressure (TMP) were investigated through two-point feeding. The results indicated that the removal efficiencies for COD and NH4+ -N were high in the system, the effluent met the requirements of the Class A in first grade discharge standard of GB 18918-2002. The effluent TN was < 15 mg x L(-1) when the reflux ratio of nitrification was 200%, whereas the average TP removal rate was 90% after the excessive sludge was removed. The effluent SS was < 10 mg x L(-1) before the large-scale breakage of membrane. The TMP increased gradually with the operation of the system, if the way of aeration was not correct, the TMP would increase quickly. Efficient separation by the membrane contributed to the removal of COD, TP and SS. Because there was no sludge washout in the system, SRT could be properly controlled, it was good for the ammonia-oxidizing bacteria and denitrifying bacteria which both have long life-cycle. Even if the inflow was increased to 1.5 fold, the effluent quality was good when the sludge concentration was increased to 6500 mg x L(-1).