Abstract: The weak impregnation will result in the formation of traps in the composites because the impregnation of the resin to fiber reinforcement is one of the major factors during the filling process of RTM. It will degrade interfacial performance of the composites. In this paper, cold plasma technology is used to treat the surface of carbon fibers braided by PET and the surface microstructure of the carbon fiber is analyzed by AFM. The result shows that cold plasma treatment improves the surface polarity of the carbon fiber, which enhances the impregnation of the carbon fiber braided by PET during the resin flowing process and improves the interfacial properties of RTM composites.