The invention relates to a surface modification method for carbon fibers. Heat convertible resin is adopted as a surface grafting material of the carbon fibers, the carbon fibers are subjected to acidizing surface treatment, then the heat convertible resin is grafted, and a high-performance composite can be formed. The surface modification method is low in cost, easy to operate and high in applicability. The surface modification method has the advantages that the equipment investment cost for carbon fiber surface modification is low, cost is low, operation is easy, high applicability is achieved, the treatment effect is good, the fiber performance loss is low, and quality is reliable. The modification time is greatly shortened, the chemical use amount is reduced, the product cost is reduced, environmental pollution is reduced, and the method is suitable for industrial production.