Within the problem of acquiring flatness and gain of Raman fiber amplifier in dense wavelength division multiplexing fiber communication system,a method is proposed to obtain higher gain and smaller gain flatness of Raman fiber amplifier by using the multi-pumped method of four pump lights and injecting two different wavelength pump lights simultaneously at the different positions of photonic crystal fiber.In Raman fiber amplifier,the optical signal is amplified in the front optical fiber and compensated in the rear optical fiber,so as to obtain high gain and small gain flatness at the Raman fiber amplifier output end.Finally,the average gain of the designed Raman fiber amplifier obtained by Matlab simulation could be 26.5 dB and the gain flatness could be 0.046 dB.