Abstract: In order to select proper space-time coding mode according to the time-varying channel, a 4×4 adaptive multi-layer space-time coding scheme was proposed in free space optical-multiple input multiple output(FSO-MIMO) based on the multi-layer space-time coding theory of antenna groups, which concludes the advantages of both orthogonal space-time block codes(OSTBC)and layered space-time code(LSTC). Simulation was carried out with Monte Carlo method. The simulation shows within a certain signal-to-noise ratio(SNR) range, the data rate can maximized at specific level of bit error rate(BER) with adaptive multi-layered space-time coding scheme.