A transmit-end device obtains a first bit sequence including K information bits (401); then maps the K information bits to m sub-blocks, and performs first polar code encoding on the m sub-blocks to obtain a second bit sequence (402); and modulates the second bit sequence to obtain and send a symbol sequence (403). Correspondingly, a receive-end device obtains the symbol sequence (404), and decodes and demodulates the symbol sequence to obtain the K information bits (405). The m sub-blocks include a first sub-block, a quantity of information bits included in the first sub-block is obtained based on K and a code rate R of the first bit sequence, m may be understood as a modulation order of the first bit sequence, and a length of the second bit sequence is N.