This disclosure provides a data retransmission method and apparatus. The method includes: A transmitting device obtains information to be transmitted for a tth time, where the information to be transmitted for the tth time includes Rt extension locations and information to be transmitted for a (t−1)th time, and the extension locations include Mt information bits and Lt check bits corresponding to the Mt information bits. The transmitting device then performs Polar encoding on the information to be transmitted for the tth time, to obtain a codeword after the Polar encoding, obtains a codeword for (t−1)th retransmission based on the codeword after the Polar encoding, and transmits the codeword for (t−1)th retransmission. A receiving device performs polar decoding after receiving the codeword for (t−1)th retransmission, to obtain a decoding result of codewords for t times of transmission. By performing, on an encoding side, check encoding on the information bits in an extension part, a decoding path can be reduced in a decoding process, thereby greatly reducing decoding complexity, and reducing storage overheads and calculation overheads.