This application discloses a method, an apparatus, and a system for processing a transmission path fault. In this application, after a first network device receives a packet, and when the first network device determines that a third network device is faulty, a difference between an initial value of a segment routing global block SRGB of the first network device and an initial value of an SRGB of the third network device is determined, and a backup path is determined based on the difference and a backup forwarding table. The first network device sends a first packet based on the backup forwarding table.