In this paper,an LDPC concatenated coded modulation scheme based on 16-QAM optical system,including the encoding and decoding algorithms,is proposed.The low complexity soft de-mapp ing algorithm is adopted and the ITU-T requirement of 100Gbit/s optical transmission systems is considered in this sch eme.The simulation results show that when bit error rate (BER) is 10－8,the net code gain (NCG) of proposed scheme is 2.8dB more than that of RS(255,9).And its NCG is 1.3dB and 0.2dB more than that of RS(255,9) +CSOC(n/k=7/6,J=8) and orthogonally concaten ated BCH code,respectively,which are two of FEC schemes with similar code-rate in ITU-T G.975.1.At the same time,the redundancy of the prop osed scheme is lower than that of the two schemes. On the other hand,the spectral efficiency (SE) of the proposed scheme is 3.28bi t/symbol.Compared with the NCG of other schemes with lower SE,such as 4-QAM,8-QAM and 8-QAM-RS(255,9),the propos ed scheme also has 3.5dB,6.4dB and 2dB additional gains,respectively.Therefore,the proposed scheme has advantages in bo th NCG and SE.