© 2021 IEEE.A broadly flatness gain band with double pass serial hybrid fiber amplifier utilizing single pump power unit is experimentally demonstrated. Simple serial hybrid fiber amplifier that consists of erbium doped fiber amplifier and Raman fiber amplifier is used. Only one Raman pump power unit of 1495 nm with maximum power of 400 mW is used for both of Erbium and Raman amplifiers. Erbium amplifier is pumped by the residual pump power of the Raman amplifier. At small input signal power of-25 dBm, and at optimum pump power, a gain flatness of 70 nm from 1530 to 1600 nm with an average power of 32 dB is obtained. In addition, at large input signal power of-10 dBm, two different flatness bandwidth regions are recorded. Flatness gain bandwidth of 52 nm (1525-1577) within C-band region with an average gain of 22 dB is achieved. Another flatness bandwidth of 40 nm (1577-1617 nm) with an average gain level of 16.5 dB was also obtained in the L-band region at the same large input signal power.