The basic process and effect of modification of polyacrylonitrile(PAN) fiber by protein surface grafting was studied in this paper. With simple procedures of surface hydrolysis, acidchloride reaction and grafting, the soybean protein could be grafted onto the PAN fiber which endowed the fiber with protein surface, and protein-modified PAN fiber was obtained. SEM photographs showed that after the protein has been grafted, the cracks and pores of the surface of the PAN fiber were filled with protein which gave the fiber new surface and structure. Thus the surface property of PAN fiber changed and the protein-modified function was obtained.