The invention discloses preparation of 3- (1,3-dithiane-2-ylidene)pentan-2,4-dione and a method for separating palladium from platinum through extraction by using the same, and belongs to preparationand use of ketene dithioacetal compounds. The compound adopts a molecular formula of C9H12O2S2, Mr 216. The preparation comprises the following steps: dissolving a certain amount of anhydrous potassium carbonate in DMF, adding a proper amount of acetylacetone, reacting for 50min, dropwise adding an equimolar amount of carbon disulfide, reacting for a certain period of time, then dropwise adding anequimolar amount of 1,3-dibromopropane, reacting for 4 hours, then washing by using water, recrystallizing and drying. The extraction comprises the following steps: preparing an aqueous phase, and keeping the pH of a palladium-platinum mixed solution at 2; preparing an organic phase, and mixing the phases according to a phase ratio of 1:1, transferring palladium from the aqueous phase to the organic phase and reversely extracting the palladium by using thiourea with the concentration of 1.0mol/L. The 3- (1,3-dithiane-2-ylidene)pentan-2,4-dione has high-efficiency palladium extracting performance in a hydrochloric acid medium, has a high palladium and platinum separating degree and has the palladium extracting rate as high as 97.58%.