A 3D display has a light grating unit inserted between a polarized light module and an image display unit. The light grating unit includes a dispersing liquid crystal unit, a microretarder unit, and a polarizing film. By controlling the dispersing liquid crystal unit of the light grating unit to be switched between a dispersing state and a transparent state, a displayed image is switched between a 2D image displaying mode and a 3D image displaying mode. The dispersing liquid crystal unit can be removed, so as to allow the image display unit to stay in the 3D image displaying mode.