By combining the membrane bioreactor of the PVDF hollow fiber membrane with the A/A/O process, a pilot test system of A/A/Omembrane process (A/A/OMBR) was constructed and employed in treating municipal wastewater in Taihu Lake Basin. According to the nitrogen removal of combined process, the nitrification rate of activated sludge in MBR was studied. The effect of dissolved oxygen concentration, influent ammonia nitrogen concentration and temperature on nitrification rate was analyzed. It is found that the average removal rates of ammonia nitrogen of combined process are 96.56% and 96.68% in summer and winter, respectively. Influent ammonia concentration has little effect on nitrification rate at low temperature of less than 15.0 ℃. Higher temperatures would speed up the nitrification rate and the nitrification rate of combined process at 30.5 ℃ was 2.6 times than that at 11.8 ℃. Compared with the conventional process, nitrification rate of combined process was 2.3 times than that in oxidation ditch. The enhanced nitrification of long hydraulic retention time formed by two nitrification phase and the role of membrane filtration in MBR offset the inhibitory effects of low temperature on nitrification rate.