High quality β-Ga₂O_3-δ films on c-sapphire substrates are deposited by pulsed laser deposition （PLD） under various oxygen partial pressures. The crystalline structure， chemometry and optical properties of the β-Ga₂O_3-δ films are investigated systematically by X-ray diffraction （XRD）， far-infrared reflectance spectra， X-ray photoelectron spectroscopy （XPS） and ultraviolet-visible-near infrared （UV-vis-NIR） transmittance spectra. The XRD analysis shows that all the as-deposited films are of unique （-201） orientation. The transmittance spectra reveal that the films exhibit a high transparency above 80% in the UV-vis-NIR wavelength region above 255 nm （4.863 eV）. Moreover， the optical constants and optical direct bandgap are extracted based on the transmittance spectra with Tauc-Lorentz （TL） dispersion function model and Tauc’s relationship， respectively. A further step， the influence of oxygen partial pressure on optical properties is explained by theoretical calculation.