This application discloses a polar code retransmission method and apparatus, to achieve an encoding gain. The method includes: when decoding of the first code word fails, performing polar code encoding on K first to-be-encoded bits and K′ second to-be-encoded bits based on a second information bit position set to obtain a second code word, where elements in the second information bit position set are used to indicate positions of the to-be-encoded bits, and an element that is in the second information bit position set and that is used to indicate a position of a first to-be-encoded bit is a sum of N and an element that is in the first information bit position set and that is used to indicate the position of the first to-be-encoded bit; and sending a subcode in the second code word other than the first code word to the decoding device.