The reflectance of thermochromatic material vanadium dioxide (VO2) and its fluctuation (noise spectrum) were measured simultaneously during the semiconductor-metal phase transition via self-built experimental system. The noise spectra were measured by a Data-Acquisition Card with real time fast Fourier transforms (FFTs-DAC) , showing the same phase-transition temperature (55 ℃) of the sample as that measured via reflectance measurement. A significant noise peak (around 15-20 MHz) was found in high temperature regime (the metal phase), while being almost flat in low temperature regime (the semiconductor phase). Such a noise peak also reflects that the low-temperature semiconductor phase and the high-temperature metallic phase have different crystal structures. Noise spectroscopy may be widely used to study phase-transtion materials.