The invention belongs to the technical field of distributed optical fiber sensing. The invention provides a Brillouin optical time domain reflector modulated by the physical random number, aiming at the compromise between the spatial resolution, the signal-to-noise ratio, and the measurement precision of the Brillouin optical time domain reflector in the prior art. The Brillouin optical time domain reflector comprises a first DFB laser emitting module, a second DFB laser emitting module, a first optical fiber coupler, a pulse optical amplifier, a second optical fiber coupler, a polarization controller, a gain switch modulator, a physical random number generating module, a DWDM dense type wavelength division multiplexer, a sensing optical fiber, an optical fiber circulator, a continuous optical amplifier, an optical filter, a third optical fiber coupler, a scrambler, a photodetector, a mixer, a microwave adjustable frequency source, an electric amplifier, an electric filter, an A / D conversion module, and a host computer. The invention can monitor the strain magnitude and location of the sensing optical fiber along the line in real time with high precision under the premise of ensuring spatial resolution.