Silicon thin films were prepared on silica substrates by ion beam sputtering, electron beam evaporation and ion assisted deposition. The transmittance spectrum, the reflectance spectrum and the ellipsometric spectrum were obtained in the wavelength region from 300nm and 2000nm, where Lambda 900 spectroscopy and VASE ellipsometer were applied. The optical constants were calculated by multiple spectrum analysis with WVASE32 which is the analysis software for ellipsometry of J.A.Woollam company. There were about ten nanometers of silicon dioxide layers on the surface of the silicon films. The near infrared extinction coefficient of the silicon thin film prepared by ion beam sputtering was the largest, followed by ion assisted deposition, the extinction coefficient of the electron beam evaporated silicon film was the smallest, and the refractive index of the electron beam evaporated silicon thin film was the lowest. The heat treatment experiments of 300°C and 400°C showed that the refractive index of the 600nm-200nm band of the ion beam sputtering silicon film decreased obviously, while the refractive index of the electron beam evaporation and the ion assisted deposition silicon thin film had little change, and the heat treatment at 300°C could significantly reduce the extinction coefficient of the near infrared band of the three silicon thin films. In the further heat treatment at 400°C, the extinction coefficient of the ion beam sputtering silicon film and the ion assisted deposition silicon film continued to decrease, while the extinction coefficient of the electron beam evaporated silicon film increased.