Embodiments relate to a data transmission method. A relay node receives information that is about an SCMA codebook used by the relay node and that is sent by a destination node. The relay node receives two or more source signals sent by two or more source nodes. The relay node performs network coding on the received two or more source signals. The relay node performs SCMA codebook mapping on a signal obtained after the network coding, so as to obtain at least two modulation symbols. The relay node sends to the destination node, the at least two modulation symbols obtained after the SCMA mapping.