The invention relates to a device and a method for preparing polymethoxy dimethyl ether, particularly relates to a device and a method for synthesizing polymethoxy dimethyl ether with medium concentration formaldehyde and methylal, solves the problems of complicated structure, high operation and maintenance costs, high energy consumption, low yield and not conducive to industrialized continuous production in the prior device, the technical scheme is that the device comprises a static mixer, one end is connected with the input tube, the other end is connected with the pipeline reactor, the other end of the pipeline reactor is connected with a refining separation device. The method comprises the steps of a, filling the reactor with catalyst; b, feeding raw materials into the mixer and mixing well; c, feeding raw materials into the reactor, controlling the temperature, pressure, liquid volume space velocity; d, separation and purification. The device and the method have the advantages of lower energy consumption, high production capacity, suitable for large-scale and continuous production, small back-mixing, sectional temperature control, low wear rate of catalyst, easy separation, no corrosion to device and simple subsequent processing, less pollution, high selectivity, low cost, few high polymer in the product and low separation and purification energy consumption.