Based on the Gamma-Gamma turbulence c hannel,an iterative detection and decoding algorithm of low-density parity-che ck ( LDPC) coded free-space optical communication multiple-input-multiple-output (FSO-MIMO) system is studied.For high complexity of the optimal maximum a poste riori (MAP) algorithm and bit nodes posterior log likelihood ratio (LLR) oscillation in BP iterative process,an improved LDPC+PDA iterative detection and decoding algorithm based on mean value of a feedback is promoted.After iteratio n process of BP decoding algorithm,the mean of posteriori information,which is the output of bit nodes wi thin each inner iteration,is taken as a feedback to detector,in order to improve the reliability of the decoder me ssages passed to the detector.The simulation results show that when the bit error rate is about 10－5,under the condition of weak turbulence,the improved algorithm has 0.3dB performance advantages compared with traditional a lgorithm.Under the condition of strong turbulence,the improved algorithm increases the gain of 0.65dB.The improved al gorithm of iterative detection and decoding can further suppress the turbulence effect and improve the performa nce of the system,especially under strong turbulence conditions without significant increase in computational complexity.