This application provides a configuration information indication method and an apparatus, which are applicable to fields such as vehicle to everything V2X, intelligent connected vehicles, assisted driving, and intelligent driving, to resolve an existing-technology problem that SL transmission causes interference to DL transmission, and effectively reduce signaling overheads. This method is applied to a first terminal device, and includes: receiving an uplink-downlink time division multiplex TDD configuration sent by a network device; and sending indication information to a second terminal device based on the uplink-downlink TDD configuration, where the indication information is carried on a physical sidelink broadcast channel PSBCH of a sidelink synchronization signal block S-SSB, and the indication information is used to indicate periodicity information included in the uplink-downlink TDD configuration.