Abstract: We proposed a novel method for designing Raman fiber amplifier (RFA) which could achieve output signal gain spectra flattening by using pump lights with different wavelengths in the same fiber. We simplified the analytical solution of steady-state stimulated Raman scattering (SRS) equation by employing the linear model of leading and trailing edge of gain spectra, and obtained a constant output signal power at the output port finally. Simulation results demonstrate that the designed RFA has advantages of flattened gain spectra, high gain as well as simple configuration. It provides a new way for the designing of gain-flattened RFA.