TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: The method comprises adding 80-85% of ethanol solution and iodine into a kettle, stirring the mixture, then adding hydrochloric acid with concentration of 36.5%, slowly raising the temperature to reflux and maintain, mixing ethanol solution and iodine with 27.5% of hydrogen peroxide, continuously refluxing for 4 hours, cooling until there is no reflow, where the ratio of salicylic acid/ethanol solution or iodide mother liquid is 1 KG/4-4.5 l, the mass ratio of hydrochloric acid and acid alkali 25-30, the mole ratio of iodine and alkali acid is 725-727/724, and the mole ratio of hydrogen peroxide and alkali acid is 1.1/1, crystallizing the mixture in a centrifugal tube at rotating speed of 30-84 revolutions per minute (rpm), heat preserving the mixture at 35-40 degrees C circulating in water for 2 hours, centrifuging the refrigerating fluid at 15 plus minus 1 degrees C to obtain 3,5-diiodosalicylic acid crude product, then collecting, adding 5% of sodium hydroxide solution in a refining kettle, stirring at normal temperature, adjust pH value of 10% sodium hydroxide aqueous solution to 5-6, stirring for 10 minutes, heat preserving for 30 minutes, then centrifuging to obtain 3,5-sodium salicylate salt, adding obtained 3,5-sodium salicylate salt with deionized water of two times, stirring and dropping in 36.5% of hydrochloric acid to adjust pH value to 1-2, separating out white solid, stirring for 15 minutes, cooling the refrigerating fluid at 15 plus minus 1 degrees C, centrifuging to obtain 3,5-diiodo sodium salicylate fine wet product, dissolving 3,5-diiodo sodium salicylate fine wet product in sodium hydroxide with amount of 1.5-1.7 l/1 KG, drying the 3,5-diiodo sodium salicylate fine wet product into a hot water circulation double cone rotary vacuum drier at pressure of -0.09 MPa, circulation water at temperature of 90-95 degrees C for 8 hours to obtain 3,5-diiodo sodium salicylate product with white crystalline purity (HPLC) of less than or equal to 99.5%, melting point of 232-234 degrees C, water content of less than or equal to 0.2%, ash of less than or equal to 0.1% and transmittance of less than or equal to 98% (500 mu m).