The invention discloses a manufacturing method of a cold cathode planar light source, sealing materials are coated at the peripheries of a front substrate and a back substrate which are equipped with electrodes, dielectric layers and fluorescent powder layers, the space between the front substrate and the back substrate is not sealed, clamps are used for accurate contraposition of the two substrates, the front and back substrates are further arranged in a closed cavity, the heating and exhaust of the interior of the cavity are carried out, when the vacuum degree achieves 10 to 10 Pa, the exhaust is stopped, a discharge gas is filled in the cavity, the gas filling pressure is 80T/Tr to 101.3T/Tr kPa by selection, T is the temperature of the substrates during the gas filling, Tr is the room temperature, the sealing materials are melt under the high temperature, the temperature of the cavity is then decreased, the sealing materials are gradually cured, thus completely sealing the front and back substrates; when the temperature is decreased to the room temperature, the manufactured cold cathode planar light source is taken out from the cavity, and the internal pressure of the light source is 0.8 to 1 atmospheric pressure. The usage of the manufacturing method can simplify the manufacturing process of the cold cathode planar light source, reduce the manufacturing cost and reduce the thickness of the planar light source.