In order to realize high transmission rate of 400 Gbit/s per wavelength in ultra-long span optical transmission system. The Optical-to-Signal Noise Ratio（OSNR） performances of high order modulation formats such as Dual Polarization-16 Quadrature Amplitude Mudulation（DP-16 QAM） and DP-64 QAM are studied at first. Then the relationship between launched optical power and Bit Error Ration（BER） is studied by experiments. Finally

the longest transmission distances are tested by using these two modulation formats and a bidirectionally Raman pumped amplifier. The test results show that the 400 Gbit/s DP-16 QAM optical transmission system can reach 286 km by using Raman optical amplifiers

and it’s suitable for most ultra-long span power communication scenarios.