A data transmission method and a data transmission device are provided. The data transmission method includes steps of: determining, by a transmitting end, a first precoding matrix and a second precoding matrix, the first precoding matrix being selected from a predefined first codebook, the second precoding matrix being acquired on the basis of CSI; performing, by the transmitting end, precoding processing on a data stream in accordance with the first precoding matrix and the second precoding matrix; and transmitting, by the transmitting end, the data streamed acquired after the precoding processing to a receiving end.