The development of optical transmission was summarized. The multiplexing system was show in detail. The concepts, characteristic, key technology, expand trend and application prospect of frequency division multiplexing, time division multiplexing, code division multiplexing and wave division multiplexing were illustrated. The development of optical transmission was summarized. The concepts, characteristic, key technology, expand trend and application prospect of frequency division multiplexing, time division multiplexing, code division multiplexing and wave division multiplexing were illustrated.