The present disclosure relates to data transmission methods. One example method is applied to a first communications device or a chip in the first communications device. The method includes obtaining first data, and sending, to a second communications device, a first message including the first data and a type identifier, where the type identifier is used to indicate a type of the first data, and the type of the first data includes at least one of user plane data, a status report, a control plane message, and a radio resource control RRC message of a terminal.