HfO2 is used as one of the most important high refractive index materials in the field of high laser damage threshold thin films. The band gap and the Urbach energy impact absorption and laser damage threshold directly. The HfO2 thin film is prepared by ion beam sputtering, and the technical parameters include the substrate temperature, the ion beam voltage, the ion beam current and the oxygen flow rate. The adjustment method for the optical gap is proposed based on the orthogonal experiment, and the Cody-Lorentz dielectric model is used to characterize the band gap and the Urbach energy. The results show that, when the confidence probability is 90%, the most influential preparative parameters for the band gap of the HfO2 thin film are listed as the substrate temperature, the ion beam current, and the oxygen flow rate. The wider band gap of the HfO2 can be obtained by the combination of the lower substrate temperature, the moderate ion beam current, and the lower oxygen flow rate. The Urbach energy is influenced mostly by the substrate temperature, and other parameters have no notable influence. The lower Urbach energy can be obtained at the higher substrate temperature, which indicates that the HfO2 thin film has lower degree of disorder.