The invention relates to a method for modifying the surface of carbon fiber coated with nano sol through plasma treatment, which comprises the following steps: firstly, nano particles are prepared into an organic solvent, a sol solution of water or a sol solution prepared by hybridization reaction of a precursor solution of organic-inorganic nano particles by the ultrasonic vibrating technology; secondly, the sol solution is coated on the surface of the carbon fiber, treated by means of spray coating and padding, and dried; and thirdly, the dried carbon fiber is placed on a special transport unit for plasma processing equipment and a plasma is sprayed on the surface of the carbon fiber to make the carbon fiber move in the plasma atmosphere, so as to generate surface modification, wherein the treating power is between 10 and , watts, and the treatment time is between 0.5 and 300 seconds. The method can effectively improve the performance of the fiber, improves the molded manufacturability and the overall properties of composite materials of the fiber, has simple technology, quick processing speed, good treatment effect and low cost, is convenient to operate and difficult to cause environmental pollution, can reduce energy consumption, and is suitable for industrial production.