Provided is a data transmission method and device. The method includes: receiving IQ data from an uplink; according to the mapping of the IQ data in a Common Public Radio Interface (CPRI) basic frame, utilizing at least one storage unit to sequence the IQ data; combining a control word with the sequenced IQ data to form CPRI data, and transmitting the CPRI data. The solution utilizes at least one storage unit to sequence the IQ data, and extracts the sequenced data for a CPRI framing operation. This solution is simple in hardware processing and low in realization complexity. The change and upgrade of the transmission bandwidth of multiple modes (single mode or mixed mode) during system upgrade only occur on software layer without affecting the realization of hardware, thus having good flexibility.