With the rapid growth of digital business, OTN technology becomes a main development direction of the next generation of transport network because of its large capacity and long-distance transmission. In large capacity of ULH, the signal quality declines and bit error rate increases due to the loss, noise, dispersion and nonlinear effect. The technologies of optical amplifier, dispersion compensation, FEC and code modulation can effectively solve the problems, improve the signal quality and system reliability, reduce the bit error rate, and achieve large capacity and long distance transmission.