Embodiments of the present invention provide a data transmission method, including: receiving, by second UE, a first message sent by first UE or a base station, where the first message includes relay request information; sending, by the second UE, a second message to the base station according to the first message, where the second message includes information indicating that the second UE requests to act as relay UE for data transmission between the first UE and the base station; and receiving, by the second UE, a third message sent by the base station, where the third message instructs the second UE to act as the relay UE.