Provided are a data transmission method and device, which relate to the field of communications. The method includes: when data is transmitted between an REC and one or more REs, arranging extended control words of the one or more REs in a plurality of superframes, wherein connotations of the extended control words at a same position in different superframes are different, and sending the plurality of superframes to an opposite end. By arranging extended control words of one or more REs in a plurality of superframes and different connotations of the extended control words at the same position in different superframes, the solution solves the problem that the requirements cannot be satisfied due to the limited number of control words in the protocol, and has the beneficial effect of increasing control words in the protocol.