Disclosed are a modulation method, demodulation method, and apparatus for multi-user information transmission. The modulation method comprises: a transmitter determines a first modulation symbol and a second modulation symbol according to a first information bit, a second information bit, and a mapping table, the mapping table being used for determining a corresponding relation between the first information bit and the first modulation symbol and a corresponding relation between the second information bit and the second modulation symbol, each group of modulation symbols in the mapping table being superposed and mapped to a constellation diagram to achieve a Gray attribute; and the transmitter superposes the first modulation symbol and the second modulation symbol to obtain a superposed symbol.