A 3D image display device includes a display module, an electrochromic module, a control unit and a sensing unit. The electrochromic module has a first electrochromic element and a second electrochromic element disposed in the different direction, and the electrochromic element is a solution type electrochromic material, and the valence of ions in the material is changed to produce a quick and uniform coloration. The display device transmits a detect signal of the sensing unit to the control unit, and the control unit controls the coloration/decoloration of the first and second electrochromic elements to switch the horizontal or vertical parallax barrier, such that viewers can view a 3D image from different viewing angles and directions.