Single-core submarine cables have more advantages in production and construction compared to three-core submarine cables, but the submarine cable faults caused by abnormal grounding circulating current in single-core submarine cables occur frequently. The operation mechanism and detection strategy of grounding circulating current of single-core submarine cable need to be further studied. A mathematical model for single-core submarine cables is established based on the impedance matrix, and the influences of factors such as armor resistivity, armor magnetic permeability, grounding resistance, and short-circuit resistance on the parameters within the impedance matrix and grounding circulating current are revealed. Combined with the practical engineering cases, the mechanism of uneven distribution of grounding circulating currents in submarine cables is analyzed, which provides reference bases for the evaluation of the operational status and maintenance of submarine cables.