Radio frequency magnetron sputtering method is used to grow nanostructured VOx thin film on silicon nitride layer. X-ray diffraction and atomic force microscope are used to characterize the crystal structure and surface morphology, respectively. The variations of square resistance and thermal hysteresis loop are studied when the film is exposed to air for a long period of time, and the effects of these variations on the performance of device are analyzed. X-ray photoelectron spectrometer and Fourier transform infrared spectroscopy are employed to investigate the differences in composition and molecular structure between the fresh and aged films. The results indicate that the increase of square resistance is due to the oxidation of vanadium ions with low oxidation states. The reason to cause the change of thermal hysteresis loop is that the molecular structure of nanostructured VOx thin film is affected by the adsorbed atoms and functional groups.