The experimental results using two different configuration on high-power Yb-doped double-cladding fiber superfluorescent source (SFS) pumped by 975 nm laser diode are reported. In single-pass forward (SPF) and single-pass backward (SPB) design, the maximum superfluorescent output power is 1.46W and 1.82W, while the slope efficiency is 23.4% and 29.2% respectively. In double-pass forward (DPF) configuration using the dichroic mirror as the front cavity mirror, the maximum superfluorescent output power is 2.12 W with the slope efficiency of 43.2%. And central wavelength of superfluorescent spectrum is 1070 nm, the flatness of output SFS spectrum is greatly improved with the 3 dB bandwidth from 11 nm to 42 nm.