Abstract: This application discloses a modulation/demodulation and encoding/decoding method and belongs to the field of communication technologies. The modulation and encoding method includes: grading to-be-transmitted bits into a plurality of levels; encoding a plurality of levels of bits obtained through grading to obtain a plurality of levels of codewords; and mapping the plurality of levels of codewords to a symbol in a staggered manner, where the plurality of levels of codewords include a first codeword, the first codeword is located at a Yth level of the plurality of levels of codewords, and the first codeword overlaps at least one codeword at any level other than the Yth level. In this way, codewords at different levels are associated by using a symbol to which the codewords are mapped, and an overlapping part between a plurality of codewords can assist in demodulating the codewords.