Vanadium thin film was grown on sapphire substrate by magnetron sputter ing.And then the film was annealed in oxygen by the rapid thermal processing to get VOx thin film whic h has the property of semiconductor to metal transition.The experiment is conducted under diff erent annealing t emperatures and different annealing time which can affect the characteristics of VOx thin film.The X-ray diffraction (XRD) is em ployed to analyze the crystalline structure of the thin film.The terahertz (THz) transmission modulation of VOx thin f ilm under laser excitation with different power is studied by THz time-domain spectroscopy (TDS).The results sh ow that the VOx thin film prepared in the experiment has the property of transition between insulator phase and metal phase.The best annealing condition of this VOx thin film is 570℃ with 60s treatment.The terahertz transmission modulation of VOx thin film under la ser excitation is high.The amplitude of modulation is 83.9%.The starting power a nd the power range of transition are low.The VOx thin film can be applied in the study of light switch and modulator.