Embodiments of this application relate to communication technologies and provide a method for transmitting or retransmitting data in a transport block. The transport block includes one or more code block groups, and each code block group includes one or more code blocks. A data processing device determines a code block group in the transport block that needs to be transmitted. Each code block in the code block group is processed by the data processing device to obtain a bit sequence. The data processing device transmits one or more bit sequences obtained by processing one or more code blocks in the code block group. The method and the apparatus provided in this application help reduce waste of air interface resources.