A data transmission method includes: receiving an uplink grant message from a network device, where the uplink grant message includes first information, and the first information corresponds to a plurality of transport block sizes; determining the plurality of transport block sizes based on the first information; determining, based on a size of to-be-sent data, a first transport block size from the plurality of transport block sizes; and sending the to-be-sent data to the network device based on the first transport block size.