Abstract: Submarine cables are important power channels and are costly.Once a failure occurs, consequences are often more serious.Therefore, it is very important to take active prevention in the failure of submarine cables through online monitoring technology.At present, there are many kinds of online monitoring methods for submarine cables, and their basic principles, main functions, and positioning accuracy are various.In order to analyze and compare the advantages and disadvantages of different online monitoring methods, and further improve the online monitoring technology level and failure location accuracy of submarine cables, the latest and mainstream submarine cables online monitoring technologies at home and abroad were investigated, and sorted out the characteristics and advantages and disadvanges of various technologies.And methods for optimizing and improving the online monitoring technologies of submarine cables were proposed.