The invention relates to a preparation method of
ultraviolet light absorber 2-phenylbenzimidazole, which specifically comprises the following steps: S1, adding 2-phenylbenzimidazole and an
organic solvent into a reaction vessel, adding a composite sulfonating agent while stirring, and sufficiently reacting; S2, standing and layering a product obtained by sulfonation reaction in S1, stirring and
quenching a lower-layer solution, separating out a
solid, and carrying out
solid-liquid separation to obtain a 2-phenylbenzimidazole-5-
sulfonic acid crude product; recycling the
organic solvent in the upper layer; and S3, putting the crude product obtained in the S2 into water, adjusting the pH value while stirring to fully dissolve the 2-phenylbenzimidazole-5-
sulfonic acid crude product, adding
activated carbon, stirring for decolorization, filtering, adding an acid into a filtered clarified solution for acidification, separating out a
solid, carrying out solid-liquid separation, and
drying toobtain the 2-phenylbenzimidazole-5-
sulfonic acid refined product. By the adoption of the preparation method, the obtained product is high in purity and good in quality, meanwhile, the waste acid generation amount is small, a pure white product can be obtained through one-time refining, and the process is simplified.