Abstract: Free Space optical communication havs many advantages, such as the small volume, the little mass, and the high data volume. Many countries nowadays focus on the development of free space optical communication techniques. Inter-satellite optical communication experimental success has built the confidence to deep optical communication techniques. The deep space optical communication technology started to develop later in China. So, refering to the system oversea is requested, such as the design of system, the selection of components and the parameters of system. This paper analyzed the MLCD are analyzed of USA in general, focused on the analysis of operational concept and principle for PAT subsystem, communication subsystem and ground terminal. The new components and new techniques used in MLCD are analyzed in details. Based on these analyses, the feasibility and reliability are also discussed.