A preparation method of phosphotungstic acid includes mixing a mixed solution containing tungsten, phosphorus and an inorganic acid with an organic-alcohol-containing oil phase for extraction, stripping the obtained supported organic phase and distilled water according to an oil phase:aqueous phase volume ratio of 3:1 to 10:1 to obtain a stripping solution; and carrying out thermal evaporation crystallization or spray drying on the stripping solution to obtain a phosphotungstic acid crystal, wherein the organic alcohol is a C7-C20 alcohol. The inventors have found out that the addition of an inorganic acid to a solution of phosphorus or tungsten and the use of an organic alcohol as an extractant can achieve simultaneous and efficient extraction of phosphotungstic acid. It has also been found that the organic-alcohol-containing oil phase has excellent selectivity for phosphotungstic acid molecules in the mixed solution.