The surface modification of carbon fiber (CF) treated by oxidation was carried out using polyetherimide (PEI) as modifier. The effects of surface treatment were characterized by infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The results show that the oxidized CF can obtain a more uniform and complete PEI modified layer. The effects of PEI and CF content on the mechanical properties, thermal conductivity and heat resistance of the CF reinforced polycarbonate (PC/CF) composites were investigated. It is found that the tensile strength of PC/CF composites is increased by 35.2%, the Vicat softening temperature (VST) is increased by about 2℃, and the thermal conductivity is increased by 13.1% after modified by PEI. The SEM images of tensile spline sections confirm that the PEI modified layer improves the interfacial adhesion of composites. The performance of PC/CF composites was analyzed based on the statistics of the length distribution of CF and the SEM images of the sample sections.