Hf∶ZnO (HZO) films were prepared on sapphire substrate by radio frequency magnetron sputtering. The effects of oxygen flow rate and annealing temperature on the microstructure and photoelectric properties of the films were studied. For better crystallinity, the prepared films were annealed at 800 ℃ for 30 min and then naturally cooled to room temperature. The microstructure and photoelectric properties of annealed films were tested and analyzed. The results showed that as the oxygen flow rate increased from 0 to 0.6 mL/min, the microstructure became denser and the resistivity gradually decreased. However, when the oxygen flow rate increased to 0.8 mL/min, the crystallinity deteriorated and the resistivity suddenly increased. The HZO film prepared at an oxygen flow rate of 0.6 mL/min obtained the best photoelectric properties. The results of the Fourier transform infrared (FTIR) spectrometer manifested that the average transmittance of this film in the 3--5 μm waveband was 83.87% and the Hall effect test results demonstrated that its resistivity, carrier mobility, and carrier concentration were 1.66×10 ^-2 Ω·cm, 13.4 cm ²·V ^-1·s ^-1, and 2.82×10 ¹⁹ cm ^-3, respectively. Meanwhile, the XRD results showed that the annealed films presented ZnO hexagonal wurtzite structure and grew in the (002) direction. The SEM results revealed the dense and uniform spherical particle structure on the surface of the films. In a nutshell, HZO films prepared at an oxygen flow rate of 0.6 mL/min and an annealing temperature of 800 ℃ can be used as the transparent window material for the 3--5 μm waveband.