The invention relates to a carbon fiber surface modification method and belongs to the field of modification of composite interfaces. In order to solve the problems of performance reduction of a carbon fiber, caused by the fact that the existing carbon fiber is seriously abraded by elemental oxygen on a near-ground space track, the method comprises the steps as follows: 1 cleaning; 2 oxidizing; 3 acylating chlorination; 4 stem grafting of bi (3-aminophenyl) phenylphosphine oxide (BAPPO). The carbon fiber surface modification method utilizes the excellent elemental oxygen resistant performance of the BAPPO, the BAPPO is grafted to the surface of the carbon fiber, the elemental oxygen resistant performance is improved, and an amino group of the BAPPO reacts with a resin matrix, so that the interface performance is improved. The method lays a certain theoretical foundation for the use of composites under the condition of the space environment.