This application discloses a method and an apparatus for adjusting a bandwidth of a transmission channel in flexible Ethernet. When the bandwidth of the transmission channel needs to be increased, bandwidths of all nodes are successively increased based on a direction reverse to a flow direction of service data, and when the bandwidth of the transmission channel needs to be decreased, bandwidths of all nodes are successively decreased based on the flow direction of the service data. In this way, a probability of a loss of service data transmitted from upstream to downstream is reduced in a process of adjusting the bandwidth of the transmission channel, and this improves reliability of service data transmission.