Due to the existence of remarkable current leakage in extra- high voltage submarine cables,the traditio-nal methods to calculate the induced current of cable sheath cannot be utilized directly.In this paper,according tothe structure characteristics and grounding mode of the extra- high voltage submarine cables of Hainan Interline Pro-ject,a new method to theoretically calculate the circulating current of sheath,which takes into consideration thespatial axial current distribution of long submarine core,is proposed,and the mathematical formula of the inductiveelectromotive force of sheath- armor layer of the cable is deduced based on the electromagnetic field theory and thecircuit laws.The results of both the on- site test and the PSCAD/EMTDC simulation demonstrate that the proposedmethod is feasible and effective,and that it may serve as an applicable method for the theoretical loss analysis ofsubmarine cables.