The invention discloses a preparation method and device of a polyoxymethylene dimethyl ether reaction raw material. The preparation device comprises a methanol oxidizer, a cooler I and a cooler II, and an extracting tower, a layering tank, a dehydrating tower, a distillation tower, an absorption device and a material intermediate tank which are connected in sequence; starting raw materials react in the methanol oxidizer and a product is cooled through the cooler II and then enters the extracting tower; an extracting agent is cooled through the cooler I and then enters the extracting tower; the materials pass through the extracting tower, the layering tank, the dehydrating tower, the distillation tower, the absorption device and the material intermediate tank in sequence and then are discharged to a polymerization reaction device for preparing polyoxymethylene dimethyl ether at the outer part. According to the method, formaldehyde concentration and dehydration are carried out through physical decompression and extraction, and pure formaldehyde gas without water is prepared through reduced pressure extraction and is absorbed by the absorption device to provide negative pressure for the distillation tower; a vacuum unit is not used, and the temperature of the distillation tower is reduced; the method also guarantees that the formaldehyde gas is completely absorbed by working liquid, and the working liquid absorbing the formaldehyde gas is used as a raw material for preparing the polyoxymethylene dimethyl ether, so that a plurality of purposes are realized.