Embodiments of this application relate to the field of communications technologies, and provide an encoding and decoding method and apparatus, to reduce encoding/decoding complexity and improve encoding/decoding performance. In the method, a transmit device may obtain N to-be-encoded vectors. The transmit device may encode the N to-be-encoded vectors based on a polar code kernel matrix, to obtain N temporary code blocks. The transmit device may respectively perform a mask operation on target bit sequences in an (n+1)th temporary code block to an (n+M)th temporary code block and a source bit sequence segment of an nth temporary code block, to obtain M mask bit sequences. The transmit device may respectively encode the M mask bit sequences based on the polar kernel matrix, to obtain M encoded mask bit sequences. The transmit device may sum the M encoded mask bit sequences and M temporary code blocks, to obtain M first code blocks.