The experimental investigations on double-pass backward Erbium-doped superfluorescent fiber source(DPB SFS) were presented. The depencence of the mean wavelength, spectral linewidth, and thermal stability on the Erbium-doped fiber length were measured. The source intrinsic thermal coefficents for several fiber length were measured by rapidly cycling the fiber temperature between -20℃ and 60℃. The curve of the intrinsic thermal coefficient and the stability of DPB SFS mean wavelengh versus fiber length under several temperature point were obtainted. The result of experiments has significent reference value to the selection of devices and proper design of Erbium-doped superfluorescent fiber sources.