PolyvinyIidcncnuoride(PVDF)hollow fiber ultrafiltration membrane is frequently employed in water treatment.However,the fouling of ultrafiltration membranes affects the economic effectiveness of such process significantly.The ultrasound generated by flat plate transducer(UFPT) was used to clean the polluted PVDF ul-the membrane surface were studied.The new membrane was easy to be polluted by the saturated CaClz solution.A flux Could be recovered about 81%.The flux recovery of old membrane polluted was increased to 73.2%after 7 hsoaking in citric acid aqueous solution.but its flux recovery without soaking was only increased to 56.2%.