The invention relates to the technical field of the optical fiber communication, and is a suppression method and system of relative phase noise in a coherent optical fiber Raman amplification system.The method comprises the following steps: step one, a beam splitter receives forward Raman pumping light and performs the light splitting; step two, a transmitting end beam combiner couples 99% of forward Raman pumping light; step three, an optical power meter monitors the power of the 1% of forward Raman pumping light in real time; step four, an optimal value of the optical power is determined through a feedback algorithm; step five, a fiber incident power of the transmitted signal light is regulated; step six, the forward Raman pumping light amplifies the signal light entering the transmission optical fiber; and step seven, a signal receiver receives the signal light. By improving the commercial transmitting end and the forward pumping structure at present, the forward Raman pumping light performs light splitting through one beam splitter, the fiber incident power of the signal light is regulated in real time, the compensation part reduces the noise coefficient of the Raman amplifierdue to the receiving end signal light relative phase noise caused by the forward pumping light power fluctuation.