MgO film was fabricated on （100） Si substrates with DC sputtering method, （100） highly preferred oriented MgO film and MgO/TiN bi-buffer layers were successfully obtained by optimizing the preparation parameters, and the preferred （100） orientation mechanism affected by temperature was also discussed in the paper. XRD, AFM, FESEM were used to investigate the crystalline orientation, surface morphology, as well as the cross-section morphology of MgO films deposited on substrates with and without buffer layers. Columnar structure of MgO film and a good epitaxial relationship between MgO and TiN films were shown in our samples. Refractive index of MgO film on Si was fitted with Sellmeier model in the visible wavelength range （1.692 @ 550 nm）, while on TiN/Si substrate, the refractive index was calculated to be 1.716 @ 550 nm （where part of the layer approaches to the air） with the help of an inhomogeneous model.