An interleaving and mapping method and a deinterleaving and demapping method for an LDPC codeword are provided. The interleaving and mapping method comprises: performing first bit interleaving on a check part of the LDPC codeword to obtain a check bit stream; splicing an information bit part of the codeword and the check bit stream into a codeword after the first bit interleaving; dividing the codeword after the first bit interleaving into multiple consecutive bit subblocks in a predetermined length, and changing the order of the bit subblocks according to a corresponding permutation order (bit-swapping pattern) to form a codeword after second bit interleaving; dividing the codeword after the second bit interleaving into two parts, and writing the two parts into storage space in a column order respectively and reading the two parts from the storage space in a row order respectively to obtain a codeword after third bit interleaving; and performing constellation mapping on the codeword after the third bit interleaving according to a constellation diagram to obtain a symbol stream; the permutation orders (bit-swapping patterns) and the constellation diagrams used in the interleaving and mapping processing of LDPC codes with different code rates, code length and LDPC code tables are designed and optimized using theoretical analysis. The technical solution reduces the receiving threshold of the receiving end.