The invention discloses a pressure-resistant hull material for a submarine and a preparation method thereof. The specific steps of the preparation method include: (1) preparing raw materials, and the ratio by mass percentage is: carbon nanotubes 2%~5%, manganese 0.35%~ 0.65%, chromium 2.0%~2.75%, nickel 0.6%~1.0%, molybdenum 0.9%~1.2%, tungsten 2%~4%, rare earth elements 0.6%~0.9%, and the rest is iron; Raw materials such as iron, manganese, chromium, nickel, molybdenum, tungsten, ytterbium, rhenium, and cerium are added to the vacuum chamber, vacuumed, and melted in vacuum for 1 to 2 hours; (3) refill with argon, add carbon nanotubes, and keep warm for 40 minutes ~50min, the melting is uniform; (4) Keep the pressure down to room temperature at a cooling rate of 100°C/min~110°C/min, and obtain the finished submarine pressure hull material. The submarine pressure-resistant hull material prepared by the invention has excellent pressure resistance, friction resistance, corrosion resistance, high temperature resistance and high hardness.