The invention provides a nanofiltration membrane preparation device and production process. The preparation device includes a horizontal workbench, a base, a casting liquid delivery pump, a hydraulic control valve, a casting liquid container, a casting liquid delivery pipe, and a casting liquid spraying pump. cavity, base plate, casting solution booster chamber, casting solution booster pipe, booster regulating valve and booster pump, casting solution spraying chambers are arranged symmetrically on both sides of the base, casting solution booster chamber is set on the base, and is located on both sides of the casting film In the middle of the liquid spraying chamber, the casting liquid spraying chambers and the casting liquid booster chambers on both sides are arranged in parallel, and the substrates are stacked between the casting liquid spraying chambers and the casting liquid booster chambers. A gap with a certain thickness is formed between them by a thickness adjusting device. The present invention uses the stacking with standard thickness gaps as the reaction chamber of the casting solution to ensure that the produced nanofiltration membrane has extremely high flatness, avoids problems such as pockmarks and pits, and accurately measures the nanofiltration membrane through the thickness adjustment device. The thickness of the filter membrane, and ensure that the thickness of the nanofiltration membrane is uniform.