The present disclosure relates to the communications field, and discloses a data flow transmission method, a device, and a system, so as to resolve a problem of resource waste caused when a relay user equipment provides a relay service for a remote user equipment. A specific solution is as follows: A first network device triggers a first relay user equipment to establish a common data flow bearer with a second network device, and the first network device sends an identifier of a common data flow to a remote user equipment in a first group before or after the first network device triggers the first relay user equipment to establish the common data flow bearer with the second network device. The present disclosure is applied to data flow transmission.