A thin film Of SiO2 was formed on the surface of CVD SiC fiber by electrochemical treatment. The tensile strength of the fiber was increased effectively. The formation of the thin film of SiO2 heals the surface defects and makes the surface of the SiC fiber relatively smooth. The SiO2 film also creates a compression stress on the surface of the fiber, which can alleviate the locally concentrated tension and the surface damage sensitivity. Moreover, it can also cause an additional energy consumption to overcome the surface compressive stress during tensile loading of SiC fiber.