The invention discloses an overhead line system fault identification device and a method thereof for an electrified railway AT power supply system and belongs to the technical field of alternating current electrified railway traction power supply measurement and control. An input end of the fault identification device is connected to test ends of a voltage transformer, a left adjacent AT station,an intermediate AT station, and a right adjacent AT station; the voltage transformer is connected in parallel between an overhead line system in which the intermediate AT station is positioned and steel rails; an output end of the fault identification device is connected to control ends of the left adjacent AT station, the intermediate AT station, and a right adjacent AT station; control ends of the intermediate AT include a control end of a bypass short circuiting device connected in parallel in the overhead line system where the intermediate AT is located. Therefore, the overhead line systemfault identification device and the method thereof disclosed in the present invention can help timely discover, distinguish, and isolate various overhead line system faults and calibrate specific locations of the faults; that a faultless section continues to supply power can be ensured, a power outage range can be reduced to a maximum degree, expansion of impacts caused by the faults can be prevented, and reliability of traction network power supply can be further improved.