A polar code retransmission method, comprising: performing, by an encoding device, polar code encoding on K first to-be-encoded bits based on a first construction parameter to obtain a first code word, wherein the first construction parameter comprises a first information bit position set, elements in the first information bit position set are used to indicate positions of the K first to-be-encoded bits, and K is a positive integer; sending, by the encoding device, the first code word to a decoding device; receiving, by the encoding device, from the decoding device, information used to indicate that decoding of the first code word fails; wherein the method further comprises: performing, by the encoding device, polar code encoding on the K first to-be-encoded bits and new second to-be-encoded bits based on a second construction parameter to obtain a second code word, wherein the second code word comprises the first code word, wherein K' is a positive integer, the second construction parameter comprises a second information bit position set, elements in the second information bit position set are used to indicate positions of the K first to-be-encoded bits and positions of the K' second to-be-encoded bits, 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, N is a length of a mother code obtained through encoding during initial transmission, and N is an integer power of 2; and sending, by the encoding device, a different part of the second code word other than the first code word to the decoding device. performing, by an encoding device, polar code encoding on K first to-be-encoded bits based on a first construction parameter to obtain a first code word, wherein the first construction parameter comprises a first information bit position set, elements in the first information bit position set are used to indicate positions of the K first to-be-encoded bits, and K is a positive integer; sending, by the encoding device, the first code word to a decoding device; receiving, by the encoding device, from the decoding device, information used to indicate that decoding of the first code word fails; wherein the method further comprises: performing, by the encoding device, polar code encoding on the K first to-be-encoded bits and new second to-be-encoded bits based on a second construction parameter to obtain a second code word, wherein the second code word comprises the first code word, wherein K' is a positive integer, the second construction parameter comprises a second information bit position set, elements in the second information bit position set are used to indicate positions of the K first to-be-encoded bits and positions of the K' second to-be-encoded bits, 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, N is a length of a mother code obtained through encoding during initial transmission, and N is an integer power of 2; and sending, by the encoding device, a different part of the second code word other than the first code word to the decoding device. performing, by the encoding device, polar code encoding on the K first to-be-encoded bits and new second to-be-encoded bits based on a second construction parameter to obtain a second code word, wherein the second code word comprises the first code word, wherein K' is a positive integer, the second construction parameter comprises a second information bit position set, elements in the second information bit position set are used to indicate positions of the K first to-be-encoded bits and positions of the K' second to-be-encoded bits, 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, N is a length of a mother code obtained through encoding during initial transmission, and N is an integer power of 2; and sending, by the encoding device, a different part of the second code word other than the first code word to the decoding device.