Embodiments of this application provide a data transmission method and a corresponding apparatus. The method includes obtaining, by a second terminal, first information, wherein the first information indicates a correspondence between a downlink quality of service (QoS) flow and a downlink device-to-device (D2D) bearer; and sending, by the second terminal to a first terminal based on the correspondence, a downlink data packet on the downlink D2D bearer corresponding to the downlink QoS flow, wherein the downlink data packet is carried on the downlink QoS flow.