The present invention relates to the field of communications. Disclosed are a code modulation and demodulation method and apparatus, which can improve the coding gain of a bit sequence sent by a transmit end while the diversity combination gain is obtained. The method comprises: performing channel coding on N information bits, so as to obtain a coded bit sequence; determining M1 bits used for retransmission and M2 bits not used for retransmission in the coded bit sequence; mapping, a first interweavedly-coded bit sequence that is obtained by interleaving the M1 bits, to a first set of subcarriers in a transmission bandwidth by using a first constellation diagram; repeating the first interweavedly-coded bit sequence, and mapping the repeated first interweavedly-coded bit sequence to a second set of subcarriers in the transmission bandwidth by using a second constellation diagram; and mapping a second interweavedly-coded bit that is obtained by interleaving the M2 bits, to a third set of subcarriers in the tran
