To evaluate the suitable sludge retention time(SRT)in submerged membrane bioreactor(SMBR) for drinking water treatment,two SMBRs under the SRT of 80 d and 20 d were run in parallel and compared in terms of the effectiveness for treating polluted raw water.The results showed that under the SRT of 80 d,the removal efficiencies of SMBR for DOC,UV 254,TOC,COD Mn were 19.6%,13.4%,27.7%and 30.7%,while those under the SRT of 20 d were 21.2%,13.2%,29.2%and 32.7%,respectively.Furthermore,both of the SMBRs achieved over 96%of removal for influent NH3-N.However,when the short SRT(20 d) was employed,the development rate of trans-membrane pressure in SMBR was lower than that under long SRT(80 d).Therefore,the reduction of SRT from 80 d to 20 d would not affect the effectiveness of SMBR for treating polluted raw water,but mitigate the membrane fouling in SMBR.With the short SRT,it would be possible to dose powdered activated carbon directly in the SMBR,in which the sludge withdrawal could be performed periodically,to maintain the sludge concentration in suitable range.