The invention discloses a Brillouin optical time domain analysis system based on Brillouin phase shift demodulation, which consists of two parts, namely optical path detection and circuit demodulation. The optical path adopts a symmetrical double-sideband Brillouin optical time domain analysis system, the detection light is generated by cascade modulation of a Mach-Zehnder modulator and a phase modulator, the light generated by a first-stage modulation is used as the light interacting with a pump, the light generated by a second-stage modulation is used as the auxiliary light to eliminate thephase noise, and the receiving end performs coherent detection; the circuit demodulates the signal by means of envelope detection. The Brillouin optical time domain analysis system based on Brillouinphase shift demodulation has simple system, and is easy to realize and easy to adjust; the system has the advantages of single channel, low sampling rate and small data quantity; and high Brillouin phase measurement accuracy and high stability can be obtained.