Embodiments of this application disclose a synchronization signal block determining method and a related apparatus. The method includes: A terminal device detects a first synchronization signal block (SSB); the terminal device determines a second SSB based on the first SSB, where a frequency domain position of the first SSB and a frequency domain position of the second SSB are within a preset bandwidth, or a difference between frequency domain positions of the first SSB and the second SSB is a preset value. The second SSB may be considered as a backup SSB for the first SSB.