This study reports an innovative environmental friendly polyacrylonitrile (PAN) fiber grafting modificationmethod, which is using L-cysteine as a coupling agent to link the hydrolyzed PAN fibers with protein macromolecules bycovalent bonds. After hydrolysis of PAN fibers, protein grafting was carried out after cysteine treatment. This method couldimprove the grafting efficiency of grafted polyacrylonitrile fiber without producing toxic by-products to human body andenvironment. The structure and surface appearance of the grafted fibers were characterized by FTIR, SEM, XRD and XPS. Itwas proved that the protein was successfully grafted onto the surface of acrylic fibers. The grafted fibers also showedimproved mechanical properties and good hygroscopicity.