The invention relates to an electrified relay submarine optical cable disturbance monitoring system based on shore-based detection. Frequency modulation detection optical signals of a detection lightsource enter a downlink transmission optical fiber through a downlink relay amplifier and an optical fiber interferometer. A backward Rayleigh scattering signal generated by the detection optical signal in each relay section optical fiber is coherent with a local optical signal in the optical fiber interferometer; a disturbance monitoring signal of the submarine optical cable of the relay sectionis generated, is multiplexed by a filter and an optical fiber coupler of the relay section, enters an uplink transmission optical fiber, is relayed and transmitted by an uplink relay amplifier, and istransmitted back to demodulation equipment. And the demodulation equipment distinguishes the disturbance monitoring signals of each section according to the wavelength or pulse leading edge time, analyzes and demodulates the data, and warns the safety state of the submarine optical cable of each section. Segmented detection of submarine optical cable disturbance is achieved based on the OFDR technology, disturbance monitoring optical signals are directly transmitted back to shore-based demodulation equipment, and disturbance monitoring and positioning of a long-span electrified relay submarine optical cable with the length being 1000 km or above are achieved.