A field-emission-based flat light source includes the following: a light-permeable substrate; a plurality of line-shaped cathodes; an anode; a light-reflecting layer; and a fluorescent layer. The light-permeable substrate has a surface, and the line-shaped cathodes, with a plurality of carbon nanotubes formed and/or deposited thereon, are located on the surface of the light-permeable substrate. The anode faces the cathodes and is spaced from the cathodes to form a vacuum chamber. The light-reflecting layer is formed on the anode and faces the cathode. The fluorescent layer is formed on the light-reflecting layer.