Abstract: The dependence of refractive index on spin asymmetrical coefficient was deduced based on self-averaging limit model in magnetic thin film materials with giant magnetoresistance effects and a measurement system using Fourier transform infrared spectroscopy was constructed to measure magnetorefractive effects (MRE). The measurement results of spin-valve multilayers Si/PtMn/CoFe/Ru/CoFe/Cu/Co/NiFe showed that MRE can be used to characterize GMR effect of magnetic thin films in infrared region.