A method for locating a fault of a submarine cable, a device, and a communication system are provided. A light pulse output by a Repeater (RPT) is incident to a location of a fault as a probe light pulse. The RPT obtains a time difference between the probe light pulse and the reflected probe light pulse, and sends the time difference to a terrestrial Submarine Line Terminal Equipment (SLTE) so that the SLTE may easily locate the fault according to principles of an Optical Time Domain Reflector (OTDR). Compared with the prior art, the method may locate the fault of the submarine cable more quickly and accurately, so that maintainers may maintain the submarine cable in time.