Membrane processes are more and more used in treating waste water in order to reuse, and then alleviate water scarcity problems. In this pilot test, ultrafiltration (UF) membrane was chosen as the pretreatment of reverse osmosis (RO) for the reuse of the cooling tower blowdown (CTB) of a power plant in north of China. The permeate qualities, permeability and membrane fouling of the two hollow fiber membrane modules - module A (outside-in style) and module B (inside-out style) fed with raw CTB only with a disc filter were analyzed and compared when the flux changed stage by stage in range from 60 to 110 Lmh/m(2). The results suggested that the permeate qualities of the two UF modules was similar and which could meet the requirements of the consequent RO for long-term function, module A had higher ability to resist to fouling than module B and it could run stable at or less than a flux of 90 Lmh/m(2), and module B could only do that at or less than 80 Lmh/m(2). The recovery of module A was higher, and the running capital of module A was lower.