With the rapid development of the Smart Power Bulk Transmission Systems, single-core power cables above 110 kV are used more and more widely. The circulating current, generated on the cable metal sheath, brings additional loss to the cable metal sheath and makes cable safe operation life shortened. This paper studied and analyzed how circulating current on the metal sheath of single-core cables varied with manners of arrangements, load conditions. A computation model was founded in order to calculate the circulating current. Meanwhile, relevant program had been written to make the calculation convenient and correct, which could provide evaluation criteria for the monitoring of power cables. The measured values would be compared with calculation values real-time. Once the gap between measured values and calculated values was relatively big, the operation faults would be found timely. Therefore this research could improve the security and reliability of the Smart Power Transmission Systems.