A data transmission method and a related device are disclosed. The data transmission method includes: obtaining to-be-transmitted K bits; mapping the K bits to F resource units according to a codebook and a value of the K bits, so as to obtain a codeword CK that is to be transmitted by using the F resource units, where the codebook includes S codewords in a one-to-one mapping relationship with S different values of the K bits; and sending the codeword CK by using the F resource units.