In this paper acrylic acid was grafted onto SBS powder using pre-irradiation method to produce SBS-g-PAA. The effects of monomer concentration, absorbed dose, reaction time and temperature on degree of grafting were discussed in detail. The FTIR spectra of SBS-g-PAA proved that the polyacrylic acid ha been grafted onto SBS powder successfully. Moreover, the thermogravimetry, X-rays diffraction and the scanning electron microscope were also investigated. Compared with pristine SBS powder, the SBS-g-PAA powder analysis indicated that the thermal degradation exhibited a two-step degradation pattern meanwhile the crystallinity declined and the surface became smoother because of the introduction of polyacrylic acid.Cited