Abstract: Carbon fiber has a series of excellent properties such as low density, high specific strength, high specific modulus, corrosion resistance, high temperature resistance, and good fatigue resistance. In recent years, it has been widely used in important fields such as aviation and aerospace. Compared with the high-strength medium-mold carbon fiber abroad, although there is T800 grade carbon fiber in China, the research work on high-performance carbon fiber in China has started late, and the research is not enough, and the products are not comparable to those in foreign countries. Sizing agent , as an important part of carbon fiber surface, has an important effect on the surface properties of carbon fiber and the interfacial properties of composites. The effect of sizing agent on domestic T800 carbon fiber was studied and analyzed by means of SEM, TGA and XPS. In this work, the surface characteristics of carbon fiber and the microscopic interface of the composite material has been studied, which provide a reference for the development of domestic high-performance carbon fiber products.