The invention discloses a casting method for a military ship body mold, and belongs to the field of mold casting. The casting method comprises the following steps: 1) machining a foam plate into a foam model; 2) coating the surface of the foam model with a fireproof coating; 3) drying the foam model coated with the fireproof coating; 4) burying the foam model in step 3) into molding sand and carrying out vibration molding; 5) pouring fluid metal under negative pressure to gasify the foam model; 6) after cooling a pouring model in step 5), separating a casting in a sand box from dry sand, so as to obtain a mold casting. According to the casting method for the military ship body mold, disclosed by the invention, the mold is not easily stuck with the sand in a manufacturing process, and the obtained mold has high size accuracy and a smooth surface; the finished-product mold has high fire resistance and good strength and toughness.