Ultrasonic time-domain reflectometry (UTDR) was extensively employed to visualize and analyze quantitatively the effect of aeration rate, operating flux and fiber length on sub-critical flux fouling profiles in a double-end submerged hollow fiber membrane (SHFM) module. Five 10 MHz transducers were externally mounted in contact with the outside surface of the double-end SHFM module. A single polyethersulfone hollow fiber membrane was used to filter 5 g/L yeast suspension. Results showed that the double-end SHFM module has better filtration performance by comparison with one-end SHFM module. The acoustic measurements revealed that the membrane near the upper suction end of the double-end SHFM module was more easily suffered from fouling than that near the lower suction end under sub-critical flux operation. Furthermore, the progress of foulant deposition gradually migrated from both ends to middle and reached the plateau finally. Moreover, a low operating flux was more effective to reduce membrane fouling. And a short double-end SHFM module was more easily subjected to membrane fouling than a long one at the same operating conditions. (C) 2013 Elsevier B.V. All rights reserved.