The invention relates to a preparation method of a gold salt for gold plating, particularly a preparation method of a cyanide-free gold plating reagent sodium gold sulfite, belonging to the technical field of chemistry. The preparation method comprises the following steps: gold rolling, gold bullion cleaning, gold dissolution, nitre removal, solonization, solonization, cleaning, complexing reaction, and crystallization by concentration. The method has the advantages of simple technique and high safety, can not generate dangerous intermediates in the process, can effectively lower chlorine ions, and can be used for producing the odorless green environment-friendly product.