The invention relates to a milliwatt level field emission cold light source, in particular to a method for preparing a screen printing composite nanometer SiC film and the field emission luminescent tube thereof. The field emission luminescent tube is characterized by comprising two pieces of parallel ITO conducting glass (1); a position between two pieces of ITO conducting glass (1) is sealed peripherally and vacuumized; an insulated column (4) playing the role of supporting is mounted between the two pieces of ITO conducting glass (1), a fluorescent film (3) is printed on the ITO layer of the internal surface of one piece of the ITO conducting glass (1), and a SiC film (5) is printed on the ITO layer of the internal surface of the other piece of ITO conducting glass (1); and the ITO layers of the two pieces of ITO conducting glass (1) are led out of the luminescent tube through electrodes. The method can prepare large-area uniform nanometer SiC films which can be used for manufacturing the luminescent tubes with good stability and high luminous efficiency.