Vanadium dioxide (VO 2 ) films play an increasingly important role in laser protection. The mid-infrared switching characteristics of VO 2 films are tested. The phase transition response time is measured and is at the nanosecond level. Measured at 5 wavelengths of 3.5μm, 3.7μm, 3.9μm, 4.1μm, 4.5μm and 4.7μm, the maximum of the power attenuation multiple before and after the phase change of the thin film was 13.29, and the minimum was 7.78. The switching characteristics of VO 2 films are obvious. In addition, the phase transition thresholds and damage thresholds of lasers with wavelengths of 3.7μm, 3.9μm and 4.1μm on VO 2 films were measured. It was found that with the increase of the wavelength, the thin film phase transition threshold decreased and the damage threshold increased. The film has a good protective effect on mid-infrared lasers.