Embodiments of the present invention disclose a polar code processing method and communications device. The method includes: obtaining, based on a target coded bit quantity M and preset first mapping relationship information, a first sequence number set of M uncoded bits that is corresponding to the target coded bit quantity M, the first mapping relationship information is used to indicate a one-to-one correspondence between a plurality of coded bit quantities and a plurality of uncoded bit sequence number sets, the M uncoded bits include K information bits, and M target coded bits are obtained after polar encoding is performed on the M uncoded bits; and selecting, from the first sequence number set of the M uncoded bits according to a preset first selection rule, K sequence numbers as a sequence number set of the K information bits.