We have measured a series of 3C-SiC on 4H-SiC structure thin film samples with different growth temperature at room temperature using J.A.Woollam M-2000 spectroscopic ellipsometer.Sufficient low mean square error has been reached and layer thickness,surface roughness and dielectric properties are obtained precisely by fitting using CompleteEASE software.Here we show the data of C06 which was grown at 1540 oC for 1 hour.Raman cross-section data is also presented for determination of 3C film and the thickness derived from these two methods could be comparable.