Real-time monitoring of the power cable's operation condition can timely detect the faults in high-voltage cables. This paper proposes an online monitoring method for cross-linked polyethylene (XLPE) cable based on the locus method of metal sheath parameters. Firstly, the signals of earthing circulating current and induced voltage in the sheath of power cable are measured synchronously. Then these two signals are fitted to draw a locus diagram. Based on the analysis of the characteristic parameters of the locus diagram, the insulation condition of the power cable is identified. Finally, a new ...