The invention discloses a system and a method for monitoring an optical cable of a backbone network. The system comprises a light source, an optical pulse forming unit, a photoelectric detection unit, a data processing unit, an early warning unit and a display unit; the optical pulse forming unit is used for generating local oscillation light and pulsed light according to the light emitted by the light source, the pulsed light is transmitted to a measured sensing optical cable, and backward Rayleigh scattering light generated by the pulsed light in a propagation process is sent to the photoelectric detection unit together with the local oscillation light; the photoelectric detection unit is used for carrying out coherent detection on the backward Rayleigh scattering light and the local oscillation light; the data processing unit is used for carrying out data processing on the signal output by the photoelectric detection unit and outputting a monitoring result; the early warning unit is used for carrying out fault early warning according to the monitoring result; and the display unit is used for displaying a map and locating the fault position according to the map and the monitoring result, and the map comprises a backbone network circuit and an optical cable. The system and the method disclosed by the invention are used for actively monitoring the performance of the optical cable in real time, finding faults or hidden trouble in time and carrying out fault locating and fault early warning.