The invention discloses a method for preparing a gold salt activator, which comprises the following steps: firstly, performing lamination treatment on gold to form a gold sheet; secondly, putting the gold sheet into an electrolytic tank filled with solution of potassuim cyanide for electrolysis, taking the gold sheet as an anode and electrolyzing the anode gold sheet into KAu(CN)2; thirdly, performing freezing crystallization on the electrolyzed solution of KAu(CN)2 in the electrolytic tank to obtain solution containing KAu(CN)2 crystals, filtering through a filter membrane filter, washing the filtered KAu(CN)2 with water, performing the secondary freezing crystallization and secondary filtration, heating and dissolving the filtered KAu(CN)2, performing the third filtration on the dissolved solution with the filter membrane filter, performing the third freezing crystallization on the filtered KAu(CN)2 solution, and filtering to obtain KAu(CN)2 crystals; and finally, directly baking and drying the KAu(CN)2 crystals to obtain KAu(CN)2 particles.