Provided is a physical quantity measuring method using a Brillouin optical fiber sensor. An optical fiber is set on a structure and a pair of pulse lights having different pulse widths is selected. The pulse lights are sequentially transmitted through the optical fiber to obtain back scattering lights and Brillouin gain spectra. The Brillouin gain spectra are compared to each other to calculate a normalized spectrum and a Brillouin frequency is acquired based on the normalized spectrum. The Brillouin frequency is multiplied by a conversion factor of a corresponding physical quantity of the structure to obtain the physical quantity. Accordingly, a portion of the optical fiber from which a sensing signal can be acquired is shortened to improve spatial resolution.