The invention discloses a method for preparing UV light-catalyzed carbon fiber grafted polyaniline. The method comprises the following steps: soaking chopped carbon fibers in ammonium persulfate/ferrous chloride, stirring for certain time, washing, and vacuum-drying to obtain oxidized chopped carbon fibers; pre-modifying the oxidized chopped carbon fibers with dopamine; and placing dopamine-modified carbon fibers and ammonium persulfate in a dopamine hydrochloride solution and grafting the surfaces of the dopamine-modified carbon fibers with polyaniline under irradiation of a UV lamp. In the method, the number of surface active groups of the fibers is increased firstly through oxidation, then the surfaces are modified with dopamine, and the polyaniline is polymerized to be grafted onto the surfaces of the fibers under catalysis of ultraviolet light, so that improvements on wettability and reactivity with a matrix in the later stage are favorable, and the electromagnetic wave absorption performance is greatly improved. The method has the advantages of being mild in conditions, high in grafting efficiency, relatively stable in polyaniline on the surfaces of the fibers, and capable of improving poor bonding strength with the matrix, low adhesion and the like, and is favorable for improving the performance of a carbon fiber reinforced composite material.