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 showed 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 was found that the tensile strength of PC/CF composites increased by 35.2%, the Vicat softening temperature (VST) increased by about 2℃, and the thermal conductivity increased by 13.1% after modified by PEI. SEM images of tensile spline sections confirmed that PEI modified layer improved 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.