The invention relates to a method for preparing a promoter, in particular to a method for preparing an air-tight promoter. The method for preparing the air-tight promoter is characterized by comprising the following steps of: 1, adding short fibers, asphalt, silicon and alumina powder into coal powder, proportioning and mixing, wherein the adding amount of the short fibers is in an amount which is 15 percent based on the input amount of materials; 2, adding a mixture which is metered and mixed in the step 1 into a pulverizing mill for grinding, and performing vibration sieving purification by using a screen sieve; and 3, adding treated distillate aromatic extract (TDAE) into the mixture obtained in the step 2, putting into a mixing machine at the temperature of between 40 and 45 DEG C, rotating and mixing for 1 to 10 minutes, and discharging. The method has the advantages that: the content of rubber in butyl rubber is reduced, specific gravity is low, Mooney viscosity is reduced, and extrusion rate is improved, so that the production speed and the production efficiency of a product are increased; and return rate is reduced, namely product yield is improved.