Accurate monitoring of burial depth can effectively avoid severe submarine cable failures. For existing submarine cable burial depth detections, they are not only difficult to implement but also impossible to monitor in real time. In this contribution, we propose a real-time monitoring method for the burial depth of direction current submarine cable based on the equivalent thermal circuit and optical fiber monitoring temperature: establish an equivalent thermal circuit from the built-in optical fiber to the outer sheath, use the optical fiber monitoring temperature to calculate the outer sheath temperature, then calculate the seabed soil thermal resistance from the core loss, the outer sheath temperature and the seabed surface temperature, and then calculate the burial depth of submarine cable according to the relationship between the seabed soil thermal resistance and the burial depth in IEC-60287 standard. We simulate the optical fiber monitoring temperature by finite element analysis, and put forward correction factors to determine the thermal resistance of the bedding layer and the armour layer according to the simulation results. Our results show that the maximum error of detection does not exceed 8cm when the depth of burial lies in the range from 0.5m to 1.5m under any current load.