The carbon fibers are subjected to an electrolytic oxidation that removes weak surface layers, etches the fibers, and generates reactive or polar groups. The new surface is easily wetted by thermosetting resins due to their low viscosities and bonds well to epoxy resins. This material usually does not promote adhesion but prevent fiber damage during fiber handling in filament winding, prepregging and weaving operations. The sizing best suited for a given process must be selected to maximize the speed and minimize accumulation of defects and broken fiber. Since the sizing is typically an uncured epoxy resin, it may actually interfere with bonding between the fiber and the matrix. Analytical techniques are discussed as well as how to detect possible problems.　　 In this paper, we choose Polyacrylonitrile (PAN) carbon fiber and polyurethane resin for sizing agent, the polyurethane resin emulsion sizing agents are diluted t0 2％, 3% and 4%, the process is to study two different thermosetting resin which are concentrated (2%, 3%, 4%), wet time (lOs, 20s, 30s) and the sizing of the drying temperature (80 degree centigrade, 100 degree centigrade, 120 degree centigrade).　　 After above sizing process this paper aims to study an effect of sizing on surface properties of carbon fiber and the fiber/epoxy interfacial adhesion by comparing sized and desized T300B. By means of X-ray photoelectron spectroscopy (XPS), activated carbon atoms can be detected, which are defined as the carbon atoms conjunction with oxygen and nitrogen. Surface chemistry analysis shows that the desized carbon fibers present less concentration of activated carbon, especially those connect with the hydroxyl and epoxy groups. Inverse gas chromatography (IGC) analysis reveals that the desized carbon fibers have larger dispersive surface energy. Moreover micro-droplet test shows that the interfacial shear strength (IFSS) of the desized carbon fiber/epoxy is higher than those of the T300B.