The invention discloses a device and a method for preparing 1,3,5-trioxane continuously from concentrated formaldehyde as a raw material. The device comprises a reaction and concentration system, a crystallization system and a refining system. The reaction and concentration system is mainly used for preparing 1,3,5-trioxane from concentrated formaldehyde as the raw material through a reaction under the action of a catalyst and concentrating 1,3,5-trioxane into a 1,3,5-trioxane solution with the concentration of 63% through a concentrating tower; the crystallization system is mainly used for concentrating the 1,3,5-trioxane solution with the concentration of 63% into a 1,3,5-trioxane solution with the concentration of 93% through crystallization; the refining system is mainly used for refining the 1,3,5-trioxane solution with the concentration of 93% into a 1,3,5-trioxane solution with the concentration of 99.9%, and the 1,3,5-trioxane solution serving as an intermediate product is conveyed to other devices for use. Compared with a 1,3,5-trioxane preparing route adopting extraction, the device and the method have the advantages that the flow and the operation are simple, energy consumption is low, environmental pollution caused by benzene is reduced effectively, and the device and the method are quite suitable for large-scale industrial production.