Wool fiber was grafted with chitosan coated Ag-loading nano-$SiO_2$ (CCTS-SLS) antibacterial composites under ultraviolet irradiation. The morphologies and structures of CCTS-SLS-wool were characterized by using scanning electronic microscopy, transmission electron microscopy, and Fourier transformation infrared spectrometry. The results show that a uniform and smooth antibacterial layer of 200 nm in thickness was formed on the surface of wool fiber by covalent bonding. The mechanical properties of the antibacterial wool fiber were improved. The antibacterial performance was found to be excellent, with antibacterial effect up to 90 % even after repeated washing. CCTS-SLS-wool possessed soft hand-feeling and good color.