This application discloses a submarine cable fault determining method and apparatus for realizing detecting whether a fault occurs to a submarine cable, without depending on TTE. The submarine cable fault determining method includes: receiving, by a network management system, first detection information from a first device during a first preset time, and receiving second detection information from a second device during a second preset time, where the second detection information is used to indicate whether the second device receives a first heartbeat signal from the first device through a submarine cable, and the first detection information is used to indicate whether the first device receives a second heartbeat signal from the second device through the submarine cable; and determining, by the network management system based on the first detection information and the second detection information, whether a fault occurs to the submarine cable between the first device and the second device.