After the development trend of high-speed long-haul optical communication systems and the theory of the concatenated code are analyzed, the comparative researches on the performances of the two concatenated codes of the inner-outer type and the improved interleaving type are performed in detail. The theoretical analyses and simulation results show that the inner-outer type concatenated code has the greater redundancy, and the improved interleaving type concatenated code is a superior concatenated code with the advantages of the better error correction performance, moderate redundancy and easy implementation. As a result, the improved interleaving type concatenated code can be better used in high-speed long-haul optical communication systems.