The invention discloses an S-O-Mg fireproof door core board produced in a rolling and flattening line. The S-O-Mg fireproof door core board is prepared from the following raw materials in parts by weight: 30 to 50 parts of silicon ash, 10 to 15 parts of MgSO4, 5 to 10 parts of MgO, 30 to 55 parts of water, 2 to 9 parts of palm fiber of which the length is 0.1mm to 1mm and 3 to 12 parts of modifier. A method for producing the S-O-Mg fireproof door core board in the rolling and flattening line comprises the following steps of (1) feeding and stirring; (2) paving; (3) maintaining: keeping the temperature in a maintenance vehicle to be 25 DEG C to 30 DEG C and the humidity to be 60 percent to 80 percent, and maintaining for 7 days to 28 days; (4) mechanically engraving. The S-O-Mg fireproof door core board disclosed by the invention is reasonable in formula and convenient to use; an obtained product is high in fireproof performance, large in strength, moderate in density and high in water absorption rate; production is further carried out by adopting the rolling and flattening line, so that the production efficiency is greatly increased, products can be continuously produced, corners are tidy, and no adhesion is generated.