A data transmission method and apparatus are provided. The method includes: modulating, based on a codebook, every N information bits of to-be-transmitted data into one M-dimensional modulation symbol, where the codebook is generated based on an M-dimensional modulation constellation, the M-dimensional modulation constellation includes M modulation constellations, a constellation point in an mth modulation constellation in the M modulation constellations is obtained by mapping N information bits based on an mth information bit subset, the mth information bit subset includes information bits on some locations in the N information bits, and a union set of M information bit subsets respectively corresponding to the M modulation constellations is the N information bits, where M and N are integers greater than or equal to 2, and m is 1, 2, . . . , or M; and sending the generated M-dimensional modulation symbol. The technical solutions can reduce complexity when a modulation signal is demodulated.