The present invention relates to a Golay complementary sequence-based phase-sensitive type optical time domain reflectometer. The reflectometer comprises an input light generating unit (1), a polarization-maintaining beam splitter (2), a coding sequence modulation unit (3), a circulator (6), an optical fiber to be measured (5), a zero-difference frequency shifter (6), a polarization control unit (7), a detection unit (8) and a signal demodulation unit (9). The invention also discloses an implementation method of the Golay complementary sequence-based phase-sensitive type optical time domain reflectometer. According to the Golay complementary sequence-based phase-sensitive type optical time domain reflectometer and the implementation method thereof of the invention, the detection unit adopts an I/Q demodulation system, and all optical field information, especially absolute phase information, of real backward Rayleigh scattered light can be effectively restored through a refined structure; local oscillation light gain makes the extremely weak signals of the tail end of the optical fiber become possible, and therefore, the sensing distance of the system can be prolonged.