Abstract: In order to study amplification characteristics of a multi-wavelength erbium-doped fiber amplifier (EDFA), steady rate equation for a multi-wavelength Er-doped double cladding fiber amplifier was deduced based on a single frequency amplifier and ignoring the amplified spontaneous emission (ASE). A theoretical model of EDFA was set up. The amplification characteristics of single wavelength amplification, dual wavelength amplification and four-wavelength amplification were numerically simulated and analyzed theoretically by using this model. The results indicate that, the optimum fiber length of the doped fiber amplifier is 8m in case of single wavelength injection. Unlike small signal amplification, the gain spectrum of a high-power EDFA tends to be flat in the range of 1530nm~1560nm. The difference of output power increases linearly with the increase of wavelength interval when double-wavelength signal laser is amplified by EDFA. While wavelength interval is 20nm, the maximum power difference of power balance compensation is 6.855W by adjusting the input signal power ratio. The minimum deviation of output power is 0.28W by adjusting the wavelength interval and power ratio parameter when four-wavelength signal laser is amplified by EDFA. And the gain equalization can be easily achieved within a certain range. The study will be helpful for multi-wavelength Er-doped fiber lasers and their application in laser Doppler radars.