The principle of C+L band ASE fiber light source of two-stage double-pass was investigated and optimized.The output of C+L band with high power was achieved experimentally.The output of C+L(between 1 520 and 1 610 nm) is 19.2 mW (12.93 dBm) when double-pass forward pumping is used in first stage,and the mean wavelength is 1 552.823 nm;the output of C+L(between 1 524 and 1 610 nm) is 21.13 mW (13.25 dBm) when double-pass backward pumping is used in first stage,and the mean wavelength is 1 552.925 nm.The length of two stage are individually about 7 m (lower doped) and 31 m (higher doped).Meanwhile,after the character of output spectra,efficiency of pump and flatness were discussed and compared about two kinds,the conclusion is that double-pass backward pumping of the first stage in the two-stage double-pass configuration is more perfect for the design of C+L band ASE fiber source.