In order to achieve high and flatting spontaneous radiation output, a flatting broadband light source based on 974nm pump source and Er-doped fiber with high doping density is proposed and designed. Firstly, the pump light is divided into two parts to pump Er-doped fibers. Then, the two parts of light are combined and output by wavelength division multiplexing. Finally, adjusting the length of Er-doped fiber and pump power to optimizing the output spectra. According to the result in simulation, when the pump power is 160mW, the length of Er-doped fibers are 7m and 2m, the spectra with output power of 20.348mW and bandwidth of 80nm can be obtained from 1530nm to 1610nm. The flatness of spectra from 1530nm to 1610nm is ±1.268dB. The system can output flatting wide spectra without adding filters and the length of Er-doped fiber less than 10m, which is expected to be used in optical fiber sensing system.