The present invention relates to a method for preparing 1,3,5-trioxane using a distillation tower including a reactor, a distillation section, and an extraction section. Particularly, the present invention relates to a method for preparing 1,3,5-trioxane, in which the water phase separated from the stream discharged through the extraction unit of the reaction distillation tower is used in the process of extracting 1,3,5-trioxane.
