Example methods and apparatus for processing a bit block stream are described. One example method includes obtaining a first to-be-processed bit block stream and mapping the first to-be-processed bit block stream into at least two slot bit block streams. The at least two slot bit block streams include a first slot bit block stream and a second slot bit block stream. The first slot bit block stream includes a first boundary bit block and a second boundary bit block. The second slot bit block stream includes a third boundary bit block and a fourth boundary bit block. N first bit blocks exist between the first boundary bit block and the second boundary bit block. N first bit blocks exist between the third boundary bit block and the fourth boundary bit block. The first bit block is a non-idle bit block.