Abstract: The operating condition is an important factor affecting the membrane filtration performance.Effects of filtration modes including constant pressure and constant flux on UF effluent quality and membrane fouling were investigated.Results of the pilot-scale experiment show that the removal of particulate and organic matters by UF has little difference in constant pressure and constant flux conditions.In the long period of operation,more seriously irreversible fouling can be caused by filtration in constant pressure than in constant flux condition.Membrane filtration operation can remain stable in very long period in constant flux condition by selecting a reasonable flux and cleaning method.