The invention discloses a preparation method of ultra-high purity hydrofluoric acid. The method comprises the following steps: (1) vaporizing anhydrous hydrogen fluoride, doping fluorine-containing gas containing one or more of fluorine gas, nitrogen trifluoride and oxygen difluoride to obtain first mixed gas; (2) introducing the first mixed gas into a plasma generating device to convert the impurity arsenic trifluoride, contained in the first mixed gas, into arsenic pentafluoride to obtain second mixed gas; (3) washing the second mixed gas with an aqueous solution containing metal fluoride toobtain purified hydrogen fluoride, and controlling the temperature of the aqueous solution, wherein the arsenic pentafluoride in the second mixed gas is converted into arsenate and retained in waterin the washing process; (4) selectively repeating the step (2) and the step (3); (5) dissolving the ultra-high purity hydrogen fluoride in the water and filtering to obtain purified hydrofluoric acid.The method provided by the invention is simple, efficient and low in cost, can realize continuous production, and does not bright an adverse effect to the subsequent application; furthermore, the method does not produce hazardous chemical wastes, thus being less in harm to the environment.