The invention discloses a data transmission method and apparatus. The method determines a target CTU from multiple candidate CTUs according to a first partial identifier in a terminal device identifier, where the terminal device identifier includes the first partial identifier and a second partial identifier. The method sends an uplink data packet to a network device by using the target CTU, where the uplink data packet carries the second partial identifier. According to the data transmission method and apparatus disclosed, the first partial identifier in the terminal device identifier can be implicitly indicated to reduce signaling overheads of a system.