The invention relates to a preparation method of anhydrous hydrogen chloride. The preparation method comprises a hydrogen chloride/hydrochloric acid desorption section and a hydrogen chloride drying section, wherein hydrochloric acid enters a hydrochloric acid/hydrogen chloride desorption tower, water and hydrogen chloride in a gas phase are separated through an acid/hydrogen chloride desorption tower, the concentration of hydrogen chloride at an outlet is controlled to be larger than that of vapor, and then hydrogen chloride enters a hydrogen chloride deep-desorption tower; hydrogen chloride gas in a self-desorption section enters a filler drying tower to be treated and then enter a combination drying tower to be dried, and the amount of sulfuric acid entering the tower is controlled through an on-line moisture analysis system, so that the concentration of circulating sulfur in a circulating drying tower is controlled. The preparation method is economical and reliable, the corrosion problem of equipment can be effectively controlled, the economic value of the byproduct hydrochloric acid can be greatly increased, the operation life of the device can be prolonged, and the maintenance and operation costs are reduced.