We report a wideband and almost flat spectrum supercontinuum (SC) generation by using a passive mode-locked Er-doped fiber laser (PML-EDFL) and a highly nonlinear dispersion shifted fiber (HN-DSF). The fiber laser pulses are characterized with a conventional second harmonic generation frequency resolved optical gating (SHG-FROG) method. The dependence of the SC spectral width on the HN-DSF length, the spectral stability of the generated SC spectrum, and conditions for obtaining smooth spectra without a fine structure are investigated experimentally. In this paper, wide spectrum covering 1100-1750 nm wavelength range is generated with only 8.5 cm long HN-DSF when laser is single pulse operation regime. In addition, the flat spectrum with ±1 dB uniformity was obtained at the wavelength region of 1130-1510 nm. And spectral stability is about ±0.2 dB at the uniformity wavelength region. We believe that our proposed all-fiber based SC source has many important applications in recently developed frequency-domain measurement techniques such as optical coherence tomography (OCT), Optical frequency domain imaging (OFDI), optical frequency domain reflectrometry (OFDR), and their instrumentation.