PVDF, PVP, PVDF/PVP with different blend ratios and PVDF-g-PVP graft copolymer with different grafting degree were characterized by Fourier transform infrared (FTIR). As indicated by the corresponding relationship of gravimetric analysis, FTIR is feasible for the quantitative determination of PVP in the samples. It is found that when the absorbed dose was below 26 kGy, the irradiation had little influence on the spectra of PVDF. But compared to the blend with the same content of PVP, the intensity of the special carbonyl (C=O) stretching absorption of PVP in graft copolymer significantly decreases, which suggests that the grafting degree of graft copolymer can not be obtained by the quantitative relational expression from the blending method.