Si thin film has certain absorption characteristics in visible and near-infrared bands and can be used for preparing broadband absorption film. Si thin films were deposited on fused silica substrate with different deposition process parameters by ion beam sputtering technology. Based on full spectrum numerical fitting methods with the transmission spectra, reflection spectra, and ellipsometry spectra, optical constants of Si thin films were calculated. The effects of oxygen and nitrogen flow rate on optical properties were also researched. Choosing Si and Ta2O5 thin film as high refractive index materials and SiO2 thin film as low refractive index material, broadband (1 000-1 400 nm) absorption films with the absorption rate of 2% and 10% were designed. Using ion beam sputtering technique, broadband absorption films were deposited on the fused silica substrates. For broadband absorption film (A=2%), the absorption rate at the wavelength of 1 064, 1 200 and 1 319 nm were respectively 2.12%, 2.15% and 2.22%. For broadband absorption film(A=10%), the absorption rate at the wavelength of 1 064, 1 200 and 1 319 nm were respectively 9.71%, 8.35% and 9.07%. The results are of great importance to the calibration of instrument such as absorption measuring instrument and spectroscopic instrument.