Objective To explore the experimental method that uses low intensity current (mA) treatment of carbon fiber monofilament, and to discuss the effect of electric-thermal on the physicochemical properties of the surface of carbon fibers, in order to provide theoretical basis for the electric heat damage mechanism of carbon fiber composite. Methods Constant DC precision power was used to supply electric current on T300 carbon fiber monofilaments. Scanning electron microscope (SEM) and atomic force microscope (AFM) were used to analyze the change in the surface morphology and roughness of carbon fibers. X photoelectron spectroscopy was used to characterize the surface‘s chemical property of carbon fibers before and after electric-thermal treatment. And the changes of the surface activity of the fibers were obtained. Results The surface of carbon fiber treated by different current intensity changed significantly. Many cracks appeared on the surface of 2 mA and 4 mA treated fibers, and the roughness was reduced with the increase of current. The gullies on the surface after 6 mA treatment were filled and the roughness was slightly improved. With the increase of current, the C content on the surface of carbon fibers also increased, while the content of O showed the opposite trend, the content of C—C decreased slightly, while C—O decreased significantly. Conclusion The electric-thermal load showed ablation effect on the sizing agent on the surface of carbon fibers. Unreacted sizing agent remained on the surface of carbon fibers, it also shallowed grooves, reduced roughness. As a result of the high temperature generated by electric heat, the sizing agent‘s components dropped a lot, with more of fiber‘s real body exposed, more hydroxy group converted into carbonyl and carboxyl, while the surface activity of the fiber was slightly enhanced.