In this paper,a 16×40 Gbit/s DWDM systems with a long haul(500-2 000 km) is studied and the effects of different modulation modes(Carrier-Suppressed Return-to-Zero(CSRZ),Duobinary Return-to-Zero(DRZ) and Modified Duobinary Return-to-Zero(MDRZ)) and dispersion compensation(pre-,post-and intermediate) schemes on its transmission performances analyzed.Simulation results show that when the transmission distance is beyond 1 500 km,the Four-Wave Mixing(FWM) effects are well suppresses in the MDRZ mode so that its...