A data transmission method and apparatus, and a related device, and may be used in the internet of vehicles, for example, V2X, LTE-V, or V2V, or may be used in fields such as D2D, intelligent driving, and intelligent connected vehicle. A network device may send first downlink control information to a first terminal device and a second terminal device, to indicate the first terminal device and the second terminal device to perform user cooperative transmission in a first stage. After the transmission in the first stage is completed, the network device sends second downlink control information to the first terminal device and the second terminal device, to indicate the first terminal device and the second terminal device to perform user cooperative transmission in a second stage. The network device uses a two-level scheduling manner to improve transmission efficiency in the second stage.