A retransmission method includes obtaining, by a sending apparatus, a to-be-encoded bit sequence comprising K to-be-encoded bits, where K is a positive integer. The method also includes performing polar encoding on the to-be-encoded sequence to obtain an encoded first bit sequence. A length of the first bit sequence is N0. The method also includes determining an initial transmission version RV0. The method also includes determining a length E1 of a retransmission version RV1. The method also includes determining the retransmission version RV1 based on an initial transmission code rate RO. The method also includes sending the RV1.