A data transmission method, a sending device, and a receiving device are provided. A sending device obtains information data, encodes the information data by using a quasi-cyclic low-density parity-check (LDPC) code matrix, modulates the encoded data to obtain first data, and sends the first data. A receiving device obtains second data, demodulates the second data to obtain to-be-decoded data, and decodes the to-be-decoded data by using a block matrix in an LDPC code matrix, where the block matrix is a submatrix in the quasi-cyclic LDPC matrix, and in the quasi-cyclic LDPC matrix, a row weight of a row (H−1) is greater than or equal to a row weight of a row H, or a row weight of a row (H−1) is less than or equal to a row weight of a row H. In this way, decoding efficiency can be improved.