A 3D image display device includes a backlight unit for generating an original light, a display panel, a light modulating unit, and a controller connected to the display panel and the light modulating unit. According to a first signal, the original light passes through the display panel generates a first light, the first light passes through the light modulating unit, and has a first position on an objective plane parallel to the display panel. According to a second signal, the original light passes through the display panel to generate a second light, the second light passes through the light modulating unit and has a second position on the objective plane, wherein the first position is different from the second position.