The thermal printer allows a piece of plastic film covered with cyan, yellow, crimson and black pigments to pass through the front of a print head. The print head contains about 2400 thermoelectric units. Each thermal resistor can generate 255 different temperatures. The hotter the resistance, the more pigments will be transmitted. The special paper covered with polyester resin will be dyed four times after passing through the thermal resistor four times, Then the dye is sublimated into steam and diffused to the covering layer to produce color dots, and the change of dye density is transmitted to the paper to produce continuous tones.