After a series of chemical procedures of surface hydrolysis, acidchloride reaction and grafting, Polyacrylonitrile (PAN) fiber was grafted from soybean milk and the soy protein-modified PAN fiber was obtained. The structures and morphologies of the grafted fiber were characterized by Fourier transform infrared spectroscopy (FTIR), X-Ray diffraction (XRD) and scanning electron microscope (SEM).The results show that the surface of PAN fiber was covered by soy protein overlay film. Moisture absorption and mechanical properties were investigated. The grafted PAN fiber presented better hygroscopicity and still meet the requirement for wearing.