Disclosed are a data transmission method, device, and system. The method comprises: for the transmission of random access uplink data, according to the correspondence between preambles and data resources as described by a protocol, determining the data resource corresponding to the preamble in the uplink data transmission, different preambles corresponding to different data resources; transmitting the preamble and the uplink data that uses the determined data resource. In the embodiments of the present invention, a protocol describes the correspondence between preambles and data resources. For the transmission of random access uplink data, the data resource corresponding to the preamble in the uplink data transmission can be determined, and different preambles correspond to different data resources. Thus it can be ensured that different users use different data resources to bear uplink data, thereby enabling the data portion multiplexing for multiple users.