The invention relates to the field of synthesis of an inorganic compound, and particularly relates to a preparation method of potassium hexafluorophosphate. The preparation method of the potassium hexafluorophosphate comprises the following steps: performing an initial reaction under a certain condition by taking potassium bifluoride (or potassium chloride), anhydrous hydrogen fluoride and phosphorus oxychloride as reaction raw materials to obtain a potassium hexafluorophosphate crude product, adjusting the acidity by using potassium hydroxide, eliminating iron ions, adsorbing and decoloring by activated carbon, performing evaporation and concentration on the crude product after removing impurities, and performing recrystallization to obtain the potassium hexafluorophosphate finished product. Compared with the traditional preparation method, the preparation method of the potassium hexafluorophosphate has the following advantages: the preparation method is simple in operation, mild in reaction and easy to control, and the use of a large amount of unstable, corrosive and toxic raw materials is avoided, so that the operation dangerousness is reduced; by adopting the potassium hexafluorophosphate produced by the method, the yield is up to 88 percent and the purity exceeds 99 percent.