Abstract: Silicon oxycarbide (SiC_XO_4-X) thin films, an advanced optical material, have many preferred properties, such as high thermal conductivity, low thermal expansion coefficient, high hardness and so on. SiCO thin films have been deposited using RF-magnetron sputtering technology. The influence of deposition parameters on optical properties of SiCO thin film was studied. The result showed that SiCO thin films presented excellent optical properties.Decreasing of substrate temperature and sputtering power, the rising of working pressure could improve the transmission properties of SiCO films. Different deposition rate could be obtained by varying deposition parameters. The refractive index had a wide region range from 1.80~2.20.