Abstract: The dependence of SFS performance on the length erbium-doped fiber is important for the design and optimization of SFS. The experimental investigation on single-pass Erbium-doped superfluorescent fiber source (SP SFS) was presented. The dependence of the center wavelength, spectral line width, and output light power on the Erbium-doped fiber length was measured. It is discovered that, there is an optimal-length of Erbium-doped fiber for SPB SFS. The results of the experiment are significant for the selection of devices and the proper design of Erbium-doped super-fluorescent fiber sources.