A data transmission method, wherein obtaining, by a network device, a quantity of physical resource blocks, PRBs that are occupied by first data carried in a first subframe, wherein the first data is data that is sent by the network device to user equipment; determining, by the network device, a transport block size, TBS according to the quantity of PRBs that are occupied by the first data carried in the first subframe; performing, by the network device according to the TBS modulation and coding on the first data carried in the first subframe and first data carried in a second subframe, wherein the first subframe and the second subframe are adjacent subframes; and sending, by the network device, the first subframe and the second subframe to the user equipment, wherein the first subframe is sent after the second subframe, the first subframe comprises M orthogonal frequency division multiplexing, OFDM symbols, the second subframe comprises N OFDM symbols, M and N are positive integers, and M ≥ N; wherein the second subframe is an incomplete subframe on an unlicensed spectrum; and characterised in that the determining, by the network device, the TBS according to the quantity of PRBs that are occupied by the first data carried in the first subframe comprises: determining, by the network device according to a first formula S = F ( s × a), a quantity S of PRBs that are jointly occupied by the first data carried in the first subframe and the first data carried in the second subframe, wherein s is the quantity of PRBs that are occupied by the first data carried in the first subframe, the function F() is used for performing rounding up, rounding down, or rounding off, and a is a real number greater than 1; and determining, by the network device, the TBS according to the quantity of PRBs that are jointly occupied by the first data carried in the first subframe and the first data carried in the second subframe; or wherein the determining, by the network device, the TBS according to the quantity of PRBs that are occupied by the first data carried in the first subframe comprises: determining, by the network device, the TBS T according to a second formula T = F ( t × a), wherein t is the TBS in the first subframe, the TBS in the first subframe is a TBS corresponding to the quantity of PRBs that are occupied by the first data carried in the first subframe, the function F() is used for performing rounding up, rounding down, or rounding off, and a is a real number greater than 1. determining, by the network device according to a first formula S = F ( s × a), a quantity S of PRBs that are jointly occupied by the first data carried in the first subframe and the first data carried in the second subframe, wherein s is the quantity of PRBs that are occupied by the first data carried in the first subframe, the function F() is used for performing rounding up, rounding down, or rounding off, and a is a real number greater than 1; and determining, by the network device, the TBS according to the quantity of PRBs that are jointly occupied by the first data carried in the first subframe and the first data carried in the second subframe; or wherein the determining, by the network device, the TBS according to the quantity of PRBs that are occupied by the first data carried in the first subframe comprises: determining, by the network device, the TBS T according to a second formula T = F ( t × a), wherein t is the TBS in the first subframe, the TBS in the first subframe is a TBS corresponding to the quantity of PRBs that are occupied by the first data carried in the first subframe, the function F() is used for performing rounding up, rounding down, or rounding off, and a is a real number greater than 1.