Abstract: CF has smooth surface and low reactivity due to high temperature graphitization, resulting in poor interfacial adhesion of CF composites. Heteroatom modification is one of the effective methods to improve the surface reactivity of CF. In the organic composite electrolyte solution, the surface oxidation and nitridation treatment of the high-strength and high-modulus carbon fiber (CF) were carried out by cyclic voltammetry (CV). The surface element composition and microscopic morphology of CF were characterized by XPS, SEM and Raman spectroscopy. A comparative analysis based on the obtained data reveals the nitriding mechanism of the CF surface and the source of the substance introducing the nitrogen-containing functional group. The results show that under the synergistic action of organic solvent, organic nitrogen source and S-containing ammonium salt, the surface nitrogen content of CF increases from 0.28at% to 4.77at%. When there is an appropriate amount of water in the solution, the number of oxygen-containing functional groups is significantly increased. The reaction between the acidic oxygen-containing functional groups formed during oxidation, the amino group of urea, and the ammonium ions in the solution is the key to forming C—N bonds on the surface of CFs. As the reaction time prolongs, the nitrogen-containing functional groups on the surface of the CF gradually transform from amide nitrogen to nitrogen oxides, then to pyridine and pyrrole, and finally to the graphitized nitrogen. The interlayer shear strength (ILSS) of CF/epoxy composites after constant current electrochemical treatment is 132% higher than that of untreated, and the tensile strength of CF increased slightly. The results show that the organic composite electrolyte is a mild and effective solution for electrochemical treatment of CF surface.