Combining membrane bioreactor and A²/O crafts, MB(A²/O) craft is developed to promote the technology with high efficiency for phosphorus and nitrogen removal. This report studies the performances of aerobic and anaerobic phosphorus uptake and the characters of microorganism of municipal sewage treated by MB(A²/O) craft, and analyzes its mechanism as well. The results indicate that the phosphate accumulating organisms take up 20%~40% of active sludge. There are a great deal of DPB which make use of NOx-N as electron acceptor to have denitrifying phosphorus removal and take up approximately 35. 66%~67. 83% of PAOs. The average rate of aerobic phosphorus uptake is 2. 30mgP·gMLSS^-1·h^-1, and the highest rate is 5. 44mgP·gMLSS^-1·h^-1. The average velocity of anaerobic phosphorus uptake is 1. 56 mgP·gMLSS^-1·h^-1, and the biggest rate is 1. 94 mgP·gMLSS^-1·h^-1.