With the development and application of phase sensitive optical time-domain reflectometer (-OTDR) technology, traditional amplitude demodulation method can not meet the needs of high quality sensing. Phase demodulation method has the advantages of high sensitivity and high accuracy in demodulation of phase information. In recent years, it has attracted wide attention at home and abroad. The research progress of phase demodulation in -OTDR system is reviewed. Demodulation methods based on phase generated carrier (PGC), 3×3 coupler and digital coherent input-quadrature are introduced respectively. The advantages and disadvantages of these methods are simply analyzed.