A method and device for relay transmission are provided. The method includes: a relay terminal device receives a PDU transmitted by a remote terminal device to a network device, where the adaptation layer PDU carries identity information of the remote terminal device, and the adaptation layer PDU is acquired by the remote terminal device by packaging, via a layer 2 adaptation layer, data carried in the adaptation layer PDU; the relay terminal device acquires in the layer 2 adaptation layer the identity information of the remote terminal device carried in the adaptation layer PDU; and the relay terminal device forwards, on the basis of the identity information of the remote terminal device acquired, the data carried in the adaptation layer PDU to the network device.