Methods, apparatus, and systems for data or information transmission are provided. In one aspect, a data sending method by a terminal device includes: determining indication information, determining, based on the indication information, a transport block size (TBS) used to send data, and sending the data based on the determined TBS. The terminal device can determine at least two of first information indicating that the TBS is a first TBS, second information indicating that the TBS is a second TBS, or third information indicating the terminal device to select a TBS from a TBS set as a third TBS used by the terminal device to send data. The TBS set is determined based on the first TBS, and can include at least one of the second TBS or the third TBS. The indication information includes one of the at least two of the first, second, or third information.