Broadband fiber amplifiers with materials doped with metal elements as optical media play an irreplaceable and important role in the current network hardware facilities. In this paper, based on the development of broadband fiber amplifiers and previous studies in the reference literature, this study has completed the modeling of gain spectrum of Bismuth-doped broadband fiber amplifier and its numerical simulation, mainly focusing on signal amplification in the 1200-1600nm band, and studied and simulated the relationship between gain spectrum of Bismuth-doped broadband fiber amplifier and fiber length, pumping power and ion doping concentration in this band. In the case of pumping light at a wavelength of 900nm, good gain results were obtained at the central wavelength of 1350nm. The bismuth-doped fiber performs well in terms of gain performance in the spectral range of 1200-1600 nm when the pump power is greater, the fiber length is around 3 m, and the doping concentration is approximately 0.61025. This is a brand-new, highly useful active medium for NIR lasers and fiber amplifiers.