To improve the treatment efficiency of a gas-water alternate membrane bioreactor (AMBR) and make full use of the membrane module, the efficiency of membrane surface loading on synthetic municipal wastewater treatment by the AMBR was investigated through a lab-scale experiment. The results showed that: the maximum COD, NH₄+-N and TN removal load by AMBR were 84.9,6.75 and 6.5 g／(m²·d) under the condition of intra-membrane oxygen pressure lower than 200 kPa and the C／N ratio of raw water was 10. The oxygen supply rate and nitrification rate were the main factors for COD and TN removal by AMBR separately, but both of the oxygen supply rate and nitrification rate influenced the NH₄+-N removal.