In order to study the filtration performance and filtration mechanism of porous composite filter membrane for steel industry wastewater, the wettability of water droplets and oil droplets on the composite membrane was studied by the sessile drop method. Scanning electron microscopy and EDS were used to analyze the structure and composition of the outer and inner walls of the asymmetric composite membrane before and after use. The filtration mechanism of medium solid particles and oil in oily wastewater was analyzed, and the variation of the contact angle of water droplets and oil droplets in the composite pipe filter with time was measured by video optical contact angle measuring instrument. The results showed that in the process of sewage filtration, impurities such as iron oxide, which was smaller than the micropore diameter of the film surface, entered the inside of the composite membrane. It can not flow through the composite membrane layer with water, and accumulates inside the membrane. With the increase of the use time of the membrane, the accumulation of impurities such as iron oxide in the inner of the composite membrane increases. The wettability of water droplets on the composite filter membrane was good, and the oil droplets were not wetted on the composite filter membrane.