After introducing optical multiple input and multiple output (MIMO) channel model,by feed backing high reliability of low density parity check (LDPC) decoding results to BLAST decoder,a joint detection and iterative decoding algorithm suitable for LDPC-BLAST optical concatenated space-time coding system is proposed in this paper.Using Monte Carlo Method,the bit error rate (BER) of the proposed decoding algorithm is analyzed and compared with that of the originally simple concatenated decoding algorithm.It is showed that the BER of the proposed joint detection and iterative decoding algorithm is better than that of the existing simple decoding algorithm.Besides,the influence of iterative times on the proposed decoding algorithm performance is analyzed with numerical analysis method.The results show that the number of iteration should not be too large when the system BER and decoding algorithm complexity is eclectically considered.