To investigate the transgenic expressing efficacy of helper-dependent adenoviral vector (HDAd) in vitro, we constructed a HDAd encoding enhanced green fluorescent protein (EGFP), denominated as HDAd/EGFP, performed large scale preparation and purification, and then identified the purified HDAd/EGFP under fluorescent microscope and electron microscope. After the concentration of HDAd/EGFP was determined by spectrophotometer, the transgenic expression efficiency of HDAd/EGFP was compared with first generation adenoviral vector encoding EGFP (FGAd/EGFP) in vitro. Therefore, we infected A549 cells with 2000 virus particles (vp) per cell by HDAd/EGFP and FGAd/EGFP respectively and analyzed EGFP expressing level by flow cytometry. Consequently, the fluorescent expression rate and fluorescent intensity of EGFP were higher in early infected A549 cells by HDAd/EGFP than by FGAd/EGFP. HDAd, capable of expressing transgene instantly and efficiently in vitro, is a potential vaccine vector.