The invention discloses a water-cooling die casting production process of a plate blank used for a medium plate, which is characterized in that the production process adopts the protective pouring of argon gas in the overall process of the pouring so as to realize that the contact of molten steel with the air is isolated in the pouring process after the molten steel flows out from a water gap; the protective pouring of solid covering slag is adopted to ensure the surface quality of a casting blank; and an ascending hole of flow steel is regulated to enable the molten steel to stably ascend inwater-cooling die casting, and the surface quality of the casting blank is ensured. The invention avoids the defects of skull patch, pits and the like of the surface and the defect of slag entrapmentwhen the water-cooling die casting is adopted to produce the blank of the medium plate, and the adopted protective pouring reduces the secondary oxidation of the molten steel in the pouring process, has a certain adsorption function to inclusion and ensure the quality of the blank of the medium plate. The invention is suitable for the production process of the blank of a high-alloy steel medium plate of die steel with high requirement.