The invention discloses a high-precision absolute distance measurement system based on an interferometric phase comparison method, belonging to the technical field of precision measurement. The system equals to the improvement on an absolute distance measurement system based on a traditional frequency scanning interferometry method, and comprises a single frequency tunable external cavity laser, a three-way optical heterodyne interferometer and a phase measurement comparison system. The single frequency tunable external cavity laser is used for laser frequency scanning, the three-way optical heterodyne interferometer is adopted for obtaining heterodyne interference signals of a reference interference arm, a measurement interference arm and a calibration interference arm in the process of laser frequency scanning, then the phase measurement comparison system is used for extracting interference phase drift distances of the calibration interference arm and the measurement interference arm in the frequency scanning process, the interference phase drift distances are in direct proportion with optical path differences of the interference arms, and therefore, the absolute distance can be measured by comparing the interference phase drift distances of the two paths of the interference arms. By adopting the three-way optical heterodyne interferometer and the phase measurement comparison system, the system does not need to measure an air refractive index when compared with the traditional frequency scanning absolute distance measurement systems, the system can overcome frequency drift and avoids the scanned range for measuring laser frequency, and therefore, frequency calibration devices, such as a Fabry-Perot cavity, and the like, are not needed.