Ba xSr (1-x)TiO 3 single layer and graded multilayer structure films (Ba 0.7Sr 0.3TiO 3, Ba 0.8Sr 0.2TiO 3, Ba 0.9Sr 0.1TiO 3, BaTiO 3) deposited on si(100) substrate were prepared by sol-gel technique. The variable angle spectroscopic ellipsometric spectra of the Ba xSr (1-x)TiO 3 multilayer structure film were obtained in the spectral range of 380～800nm, and the thickness and refractive index of the Ba xSr (1-x)TiO 3 multilayer structure film were determined for the first time. The results show that the thickness of multilayer structure film from ellipsometric spectra is consistent with that from RBS, and the refractive index of BaTiO 3 film in multilayer is much larger than that in single layer, but closer to that in single crysal.