The invention relates to a preparation method for a catalyst, specifically to a preparation method for a mercury-free catalyst used in the synthesis of vinyl chloride from acetylene through hydrochlorination. The catalyst of the invention comprises a carrier and three active components. The three active components are composed of a component A, a component B and a component C, wherein the component A is chloroauric acid; the component B is ruthenium chloride; the component C is copper chloride; a weight ratio of the elemental gold in the component A to the carrier is 0.01 to 0.2%; a weight ratio of element ruthenium in the component B to the carrier is 0.01 to 0.2%; and a weight ratio of copper chloride in the component C to the carrier is 0.5 to 5%. The active components are loaded on thecarrier by using an equivalent-volume impregnation process; and then drying is carried out to obtain the three-element mercury-free catalyst. The catalyst of the invention has high activity, good selectivity, low price and long service life when applied to the hydrochlorination reaction of acetylene; the catalyst can be conveniently applied to conventional industrial fixed-bed acetylene hydrochlorination reactors, and can conveniently replace existing mercury chloride catalysts without additional auxiliary procedures and steps.