A data transmission method and device are provided. The method includes: generating a first physical layer protocol data frame, where the first physical layer protocol data frame includes a first identification bit and a second identification bit, the first identification bit is used for identifying whether the first physical layer protocol data frame is a retransmission data frame, and the second identification bit is used for identifying the number of retransmissions of the first physical layer protocol data frame; and sending the first physical layer protocol data frame.