Taking account difference in sputtering rate between Cu and Al, we use a polycrystalline CuAlO2 target with a ratio between Cu and Al being 0.9 ∶1 to prepare the Cu-Al-O film by RF magnetron sputtering. The electrical and the optical properties of the thin film are influenced by the temperature of the substrate. When the substrate temperature is around 500 ℃, the film has a good transmission of 70% in the range of the visible light. Calculated by the fitted formula, the direct band gap is 3.52 eV,and it is in good agreement with the theoretical value. Near room temperature, the thin film conforms to the semiconductor thermal activation mechanism, when the substrate temperature is about 500 ℃, the film conductivity reaches 2.4810-3 Scm-1.