Embodiments of the present invention disclose a coding method. The method in the embodiments of the present invention includes: constructing a check equation based on a correspondence between a first subchannel and a second subchannel that is in a second subchannel group, where a check bit of the check equation corresponds to the first subchannel, an information bit of the check equation corresponds to the second subchannel, the second subchannel group includes at least one second subchannel, a sequence number of the first subchannel is divided by a first preset value and a remainder is a second preset value, a sequence number of the second subchannel is divided by a third preset value and a remainder is a fourth preset value, and the sequence number of the first subchannel is greater than the sequence number of the second subchannel; and performing coding by using the check equation.