The operating environment of oil-filled submarine cables is complex and changeable. During operation, they will be affected by external forces such as electricity, heat, machinery, ship anchors, and earthquakes, which will cause insulation aging, damage or even breakage, reducing operational reliability, and causing breakdown accidents in severe cases. In order to effectively grasp the operating status of submarine cables, it is important to study the integrated online monitoring technology of oil-filled submarine cables. In accordance with the actual operation and monitoring requirements of submarine cables and the special structure of oil-filled submarine cables bundled with communication optical cables, this paper carried out the research of distributed optical fiber temperature sensing technology based on Brillouin optical time-domain analysis, and established a charging system based on the IEC60287 thermal circuit method. The thermal circuit model of the temperature and thermal field distribution of the oil submarine cable, a comprehensive online monitoring system for the operation of the 500kV oil-filled submarine cable has been developed, and the on-site installation and network operation of the system have been completed. The system can monitor the operating parameters of the submarine cable in real time, such as temperature, oil flow, and oil pressure. Through the analysis of historical data of the submarine cable temperature, oil flow and oil pressure, it shows that the system can monitor the operating status of the submarine cable in real time and operate stably and reliably.