A kind of combinatorial material methodology, also known as continuous compositional spread method, was employed to investigate the relationship between the optical band gap and composition of SiC thin films. A wide range of Si x C y thin films with different carbon contents have been successfully deposited in a single deposition by carefully arranging the sample position on the substrate holder. The films were characterized by surface profiler, x-ray photoelectron spectroscopy, ultraviolet-visible spectroscopy, fourier transform infrared spectroscopy and Raman spectroscopy. The carbon content y increases linearly from 0.28 to 0.72 while the sample position changed from 85 to 175 mm, the optical band gap changed between 1.27 and 1.99 eV, the maximum value corresponded to the stoichiometric SiC sample at the position of 130 mm, which has the highest Si−C bond density of 11.7 × 10 22 cm -3 . The C poor and C rich Si x C y samples with y value less and larger than 0.5 were obtained while samples deviated from the position 130 mm, the optical band gap decreased with the Si−C bond density.