This application provides a data transmission method, an access network device, and a terminal. The method includes: receiving, by a first terminal, first instruction information from a first access network device, where the first terminal accesses the first access network device, and the first instruction information is used to trigger the first terminal to connect to a second terminal; connecting, by the first terminal, to the second terminal based on the first instruction information; and performing, by the first terminal, data transmission with a second access network device by using the second terminal, where the second access network device is configured to transmit data between the first access network device and the first terminal. In this way, the first access network device and the second access network device can both provide a data transmission service for the first terminal, thereby improving communication quality of the first terminal.