Abstract: Dynamic mechanical thermal analysis(DMTA), scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) were used to study the surface of polyacrylonitrile (PAN)-based carbon fiber(CF) treated by electrochemical oxidation. The results show that the loss tangent(tanδ) of treated carbon fibers reinforced epoxy declines to 30% compared with the untreated in DMTA chart, and the change of glass transition temperature (T_g) and the peak of tanδ can availably characterize the electrochemical treatment effect of carbon fiber surface, which corresponds to SEM analysis. Quantitative analysis results reveal that the interfacial adhesion parameter A and α can reflect the interfacial bonding effect between carbon fibers and epoxy, which is compatible with what is reflected by the ILSS value of CFRP. XPS analysis indicates that the hydroxyl group content and actived carbon atom of the treated CF are higher than those of the untreated CF, which is improved to 55% and 18% respectively. Appropriate oxidative conditions can make interlaminar shear strength (ILSS) increase over 20%.