Abstract: The relationship between the amplitude reflectivity of linear polarized light and the refractive index of medium material was studied. A method was presented for measuring refractive index of medium materials. The relationship between the isotropic medium reflectivity of linear polarized light and the refractive index was derived from Fresnel formula. The principle on measuring refractive index of medium basedon reflectivity of linear polarized light was given. The configuration of the experimental installation was introduced. The variation curve was measured for the amplitude reflectivity of linear polarized light of P component and S component with changing angles of incidence. The refractive index of the materials was obtained according to the variation curve. The results show that a good agreement between experimental data of medium materials and the theory predictions is reached. The scheme is proved feasible.