The combined processes of powdered activated carbon/biological powdered activated carbon- ultrafiltration (PAC/BPAC-UF) were used to treat secondary effluent. In this study, the effect of PAC and BPAC on membrane flux, membrane resistance and the removal of different molecular weight organic compounds were investigated. In addition, the structure characteristics of the microorganisms of the BPAC were analyzed. The results showed that the optimum dosage of PAC and BPAC was 10 mg/L and 40 mg/L respectively. The reversible membrane fouling resistance of BPAC-UF was higher than that of PAC-UF, and the two processes had the least irreversible resistance at the best dosage. The biodegradation of BPAC increased the concentration of small molecular weight organic matter up to 10,000 Da in the membrane effluent. So the dissolved organic carbon (DOC) removal effect of BPAC-UF process worsened. Microorganisms such as Proteobacteria, Bacteroidetes, Planctomycetes and other microorganisms on the surface of the BPAC enhanced the removal of organic matter in water. The results of scanning electron microscopy (SEM) scans showed that there was net mucus membrane on the UF membrane surface before the backwashing of the BPAC-UF process which increased the proportion of reversible pollution resistance. The physical flushing effect of BPAC-UF was better than that of direct UF and PAC-UF processes.