The invention discloses a protein fiber antibacterial finishing method based on enzymatic grafting copolymerization. Protein fiber antibacterial finishing is performed by using of tyrosine phenol lyase for catalyzing serine in protein fiber macromolecules to be converted into tyrosine and use of horseradish peroxidase for catalyzing graft copolymerization of the tyrosine in protein fiber and vinyl-containing quaternary ammonium salt monomers. The method specifically comprises the following steps: (1) oxidizing pretreatment; (2) enzyme-catalyzed amino acid conversion; and (3) enzyme-promoting graft copolymerization of the protein fiber and the vinyl-containing quaternary ammonium salt monomers. Compared with a traditional method for carrying out the protein fiber antibacterial finishing through padding baking, high-temperature bonding or coating finishing, the method has the advantages of being low in energy consumption, good in antibacterial effect and small in fiber damage.