In order to solve the natural narrow bandwidth of wide-bandwidth optical source with Er³⁺-doped fiber amplified spontaneous emission, the configuration of double-pass, backward pumped, and connected unpumped-fiber was proposed to eliminate the influence of pump source and broaden its bandwidth. The numerical simulation and experiment were carried out. The influence of Er3+-doped fiber length and reflection coefficient of fiber reflect mirror on the optical spectrum was analyzed in detail. The optimization effect of unpumped Er3+-doped fiber on the amplified spontaneous emission output spectrum was studied. The results show that, with increasing the length of pumped fiber, the C-band of the amplified spontaneous emission spectrum decreases slowly, and L-band raises. When the reflect coefficient of mirror increases, the bandwidth of amplified spontaneous emission was broadened correspondingly. The bandwidth of amplified spontaneous emission is 50.31 nm when the pumped and unpumped fiber is 6 m and 2 m respectively, which is improved 44 nm. All the results obtained could provide support for the design of wide-band optical source.