This application provides a polar encoding and decoding method, a sending device, and a receiving device, to help overcome disadvantages in transmission of medium and small packets, a code rate, reliability, and complexity in the prior art. The method includes: pre-storing, by a computing device, at least one mother code sequence, wherein each mother code sequence comprises at least one subsequence and at least one subset, the at least one subsequence and the at least one subset each comprises one or more sequence numbers corresponding to one or more polarized channels, and wherein the one or more sequence numbers in each subsequence are arranged in an ascending order according to reliability of the corresponding one or more polarized channels; determining, by the computing device, a set of information bit sequence numbers from the at least one mother code sequence based on a code length of a target polar code; and performing, by the computing device, polar encoding on information bits based on the set of information bit sequence numbers.