Embodiments of the present invention provide a bit block processing method. The method includes: sequentially receiving a first tag bit block and N data bit blocks through a first port, where the first tag bit block includes a first length field; sequentially sending the first tag bit block and M data bit blocks in the N data bit blocks through a second port; and sequentially sending a second tag bit block and L data bit blocks in the remaining N−M data bit blocks of the N data bit blocks through the second port, where the second tag bit block includes a second length field, a value of the first length field is greater than a value of the second length field by M, and M, N, and L are all integers greater than or equal to 0.