In order to realize a high flattening C+L band amplified spontaneous emission (A SE) light output,an erbium-doped Fiber (EDF) broadband source using just one 976nm Laser Diode (LD) is proposed theoretically and demonstrated experimentally, and the theoretical analysis and experimental verification are presented in deta ils.Firstly,based on the energy level of Er³⁺,the method of realizing C+L band ASE output is presented.Then,the system configur ation is designed.One 976nm LD is used for pumping,and the pump light,which is divided into two parts by one coupler,is pumped into two EDFs with the same concentration. A fiber loop mirror (FLM) is used to improve working efficiency,and two wavelen gth division multiplexers (WDMs) are also used to couple light into EDFs.Meanwhile,an optical isolator is used to avoid the e ffect of reflected wavelength from output facet.Finally, based on the mathematical model of the ASE gain,the length of EDF is discussed as well.A high flattening C+L band ASE source is achieved by optimizing the length of EDF1which is used to control the power of C band output and the length of EDF2which is used to control the power of L band output.In the experiment,2m EDF1and 16m EDF2a re adopted.The flatness of the spectra from 1540nm to 1610nm is ±0.525dB,and the flatness is ±1.119dB during 1520-1610nm without any f ilter.The high flattening C+L band ASE output is achieved by just one 976nm LD,which can optimize system and reduce the cost as well.