The invention provides an operation state monitoring method of a railway through line cable and belongs to the field of on-line monitoring of the railway through line cable. The operation state monitoring method comprises a high-speed railway through line cable and is characterized in that by detecting a bus PT zero-sequence voltage transient-state signal of the railway through line cable is generated or not, whether an instantaneity transient-stat fault occurs to the high-speed railway through line cable is judged; and by monitoring and recording electromagnetic transient-state signal which is generated by the high-speed railway through line cable and flows through a metal shielding layer, fault early warning is performed on the high-speed railway through line cable and the fault point distance is indicated. Compared with the original cable operation state monitoring method, the operation state monitoring method provided by the invention is advantageous in that early warning can be given to an instantaneity transient-stat grounding fault before a cable is damaged; non-fault disturbance signals generated by passing of a train, reclosing and the like can be filtered; system misinformation caused by disturbance is effectively reduced; alarm accuracy is improved; and false alarm rate is reduced.