Aiming at the problem of limited input power of 10 Gb/s ultra-long distance optical transmission system, a method to suppress stimulated Brillouin scattering(SBS) and improve input power is proposed. This method effectively combines the two ways of improving SBS threshold, which are laser low frequency disturbance and signal light phase modulation, and carries out comparative experiments. The experimental results show that this method can effectively improve the SBS threshold and increase the input power of 10 Gb/s ultra-long distance optical transmission system from 12 dBm and 17 dBm to 19 dBm, thus further extending the system's relay-free transmission distance.