The invention provides a method for preparing alcohol. The method comprises the following steps of: pulverizing raw materials of potatoes, mixing pulverized products with enzyme, carrying out enzymolysis in an enzymolysis device to obtain enzymolysis products and fermenting the enzymolysis products, wherein the step of pulverizing the raw materials of potatoes comprises the processes of pulverizing the mixture of particles of potatoes and grains of sand and obtaining the particles of potatoes and the grains of sand through separation; the enzymolysis device comprises a flash tower, a heat source, an enzymolysis tank, a source of materials and a vacuum pump, the flash tower comprises a first interface, a second interface, a third interface and at least one discharge opening, the source of materials is communicated with the flash tower through the first interface, the enzymolysis tank is communicated with the discharge opening of the flash tower, the vacuum pump is communicated with thesecond interface of the flash tower, and the heat source is communicated with the third interface of the flash tower. The method can realize continuous production and energy conservation.