The arbitrary channel space of two kinds of fibers and the steady-state analytical results of the unidirectional Stimulated Raman Scattering(SRS) of N-channels are given by using the photon transfer theory and a novel gain-flattened broadband Fiber Raman Amplifier(FRA) presented.The 64-channel WDM system is simulated and a new method for the gain flattening of FRA provided.