The application of DC submarine cable in our country is still in its infancy, lack of operating experience. Due to the complexity of the sea environment, the routine inspection is difficult, making it imperative that the on-line monitoring methods of DC submarine cable to be studied. Distributed optical fiber technology is a new kind of optical sensing technology which has made a great improvement in recent years. Distributed optical fiber technology can realize online measurement of temperature, stress and strain. In this paper, an integrated online monitoring system of HV DC submarine cable base on distributed optical fiber sensing technology is described. It comprehensively uses BOTDA, ROTDR and φ-OTDR principle of optical cable, which can realize the monitoring the temperature, stress and disturbance during the operation of DC cable. At the same time, AIS function is also incorporated in the system which can fulfill the monitoring of ships in the concerned area. The distributed optical fiber sensing system ensures the safe and stable operation of DC submarine cable. In the end of the paper, the operation data of ±160kV DC submarine cable of Nan’ao HVDC project are analyzed to verify the effectiveness of the system.