To investigate the phase transformation characteristics of vanadium dioxide thin film irradiated by infrared laser, the experiment was carried out based on pump probe method. First, three groups of VO2 monocrystalline epitaxial thin films with thickness of 20 nm, 40 nm and 60 nm were prepared by oxy-molecular beam epitaxy, moreover, the CO2 continuous laser with 10.6 μm was used as the pump beam, nanosecond pulse laser with 1 064 nm and 3 459 nm wavelength were used as probe light respectively, and the three groups of films were irradiated respectively. It was found that the mean values of transmittance reduction of 1 064 nm probe laser after phase transformation of the three groups of films were 5.26%, 6.2% and 8.92%, respectively, and the reflectivity reduction was 3.09%, 6.56% and 4.93%, respectively; for the 3 459 nm probe laser, the mean values of transmittance reduction were 28.4%, 47.78%, 55.13%, and reflectance increase were 6.65%, 17.87% and 7.49% respectively. The results show that the incident laser before and after the phase transformation of VO2 thin films prepared by molecular beam epitaxy were both mirror reflected; the phase transition properties of 1 064 nm probe were not as significant as that of 3 459 nm probe; the increase of film thickness will reduce the transmittance before the phase change, while the decrease after the phase change is more obvious; before and after the phase transition, the film keeps almost opaque to CO2 laser. The investigation will provide a reference for the application of film.