To improve the gain bandwidth,output gain and gain flatness of Raman Fiber Amplifier (RFA),an Erbium doped tellurium based fiber is used as the amplification medium to design a Raman Fiber Amplifier which can realize the smooth amplification of 100 nm bandwidth signal in C+L band.During the design process,the nonlinear optimization and combinatorial optimization problems in Raman Fiber Amplifier model,immune algorithm is used to optimize the wavelength and power of pump light,and ensure the output of Raman Fiber Amplifier with high gain and low gain flatness at the same time.By MATLAB numerical simulation,the average gain of the designed Raman amplifier is 35.46 dB,and the gain flatness is 0.85 dB.