A broken wire detection system of prestressed concrete cylinder pipe （PCCP） pipeline combined with phase‑sensitive optical time domain reflectometry （Φ‑OTDR） and Mach‑Zehnder interferometer （MZI） which reduced the amount of data computation by 40% through inducing optimized in‑phase quadrature （IQ） demodulation algorithm was designed. The results of the experiment showed 20 kHz frequency response and ±2 m spatial positioning error over 20 km long fiber for single-end measurement which indicated the system could position broken wire incidents along long distance and distinguish characteristic frequencies of vibration incidents. The proposed method provided a reliable technical means for online structure health detection with full lifecycle coverage of PCCP pipeline.