A series of poly(acrylic acid)(PAA)-graft-polypropylene membranes was prepared by UV-irradiation.The water flux of original PP membrane shows independence on pH and a linear increase with the rise of operating pressure. While the grafted membranes present great sensitivity to pH and a nonlinear relationship with operating pressure. As pH rises, grafted membranes are observed a rapid drop in flux since grafting PAA chains change from coiled to extended and then cause the decrease of pore size. It is evaluated by the change ratio of pore size that pH-sensitivity of grafted membranes increase with the rise of grafting degree till 17%. Furthermore, during Cross-flow microfiltration, the grafting chains on membrane surface tend to be bent at high operating pressure, so that membrane pores are partly blocked to cause a nonlinear rise of flux with operating pressure. In a conclusion, water permeability of grafted membranes greatly rely on the conformational change of grafting chains. These conformation alteration caused by pH or pressure may provide a new approach to control membrane filtration behaviors.