The embodiment of the invention provides a flat battery which comprises a cathode structural layer, a first separation membrane coated on the cathode structural layer, a chlorophyll coating layer coated on the first separation membrane, a second separation membrane coated on the chlorophyll coating layer, an anode structural layer coated on the second separation membrane, an upper plate, and a lower plate. The cathode structural layer, the first separation membrane, the chlorophyll coating layer, the second separation membrane, and the anode structural layer are sandwiched between the upper plate and the lower plate. According to the flat battery provided by the embodiment of the invention, pollutants in traditional batteries are replaced by natural environment-friendly substances. When the battery runs out, even if the battery is discarded, environment pollution is not caused. The environment friendliness of the battery is greatly higher than that of traditional batteries.