Abstract: The PAN-based carbon fiber(CF)bundles with 12K were treated continuously by a new equipment of electrochemical modification in 10%(mass fraction) NH₄HCO₃ electrolyte solution to improve its interfacial bounding strength without compromising the tensile strength simultaneously. SEM, XRD, XPS and Raman spectra were employed to characterize the morphology, chemical states, crystallites size and ordered degree of the CF surface. The results indicate that the interlaminar shear strength(ILSS)of CF/resin composites increases by 23.3% while its tensile strength only decreases by 4.4% under the optimal modified condition. The improvement of interlaminar shear strength causes not only by the increase of surface roughness, but also by the interaction effects of oxygen-containing and nitrogen-containing functional groups on CFs. After electrochemical oxidation the crystallites size decreases by 6.3%~27.6%, and the ordered degree on CF surface increases with the suitable etching which does not peel off the ordered region on the CF surface and creates new cracks; both above reduce the loss of tensile strength.