Abstract: The ability and characteristic of each electrolyte to oxidize carbon fiber(CF) were investigated by multi-scan cyclic voltammetry. The effect of different electrolytes on mechanical performance of high strength and high modulus CF with anodic oxidation surface treatment were discussed. The suitable parameters of surface treatment for high strength and high modulus CF were proposed. The effect of electrochemical oxidation on the surface structure and mechanical performance of high strength and high modulus carbon fibers were discussed using laser Raman spectroscopy, XPS and SEM. Compared with NH₄H₂PO₄ solution, the surfacial functional groups containing oxygen in the fiber significantly increases in the mixed electrolytes of NH₄H₂PO₄ and CH₃COONH₄, and the relative content of sp² hybrid carbon atom is higher. The interlaminar shear strength(ILSS) of CF/epoxy composite is improved and the mechanical performance of CF is kept at the same time. When the mole ratio of CH₃COONH₄ to NH₄H₂PO₄ is 2∶1 in the mixed electrolytes, the ILSS of CF/epoxy composite increases by 168% and the tensile strength little decreases compared with untreated fiber. Therefore, it is a good electrolyte for surface treatment for high strength and high modulus CF.