Aiming at the problem that the frequency synchronization of communication optical cable fault monitoring is limited by the length of optical cable, and the monitoring accuracy is easy to decline, a fault monitoring method for ultra-long-distance communication optical cable based on wide area measurement is proposed. In this method, the global positioning system(GPS) precise synchronous vector measurement unit (PMU) is used to provide frequency, phase and amplitude information, and the optical time domain reflectometer (OTDR) technology is used to determine the optical cable fault point, and the ultra long distance optical cable fault monitoring is completed. The experimental results show that: the frequency of optical cable fault signal changes obviously, and the fitting degree with the actual monitoring results is higher than 90%, the measurement time is short, and the monitoring effect of ultra -long-distance communication optical cable fault is better.