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The invention discloses a medium silicon molybdenum niobium spheroidal graphite cast iron material and a preparation method thereof. The medium silicon molybdenum niobium spheroidal graphite cast iron material is prepared from the following chemical components in percentage by mass: 2.8-3.2% of C, 4.2-4.5% of Si, less than or equal to 0.4% of Mn, less than or equal to 0.04% of P, less than or equal to 0.015% of S, 0.8-0.9% of Mo, 0.6-0.9% of Ni, 0.4-0.7% of Nb, 0.03-0.06% of Mg, 0.15-0.25% of V and the balance of Fe and inevitable other elements. Since C04 high-purity pig iron and waste steel are taken as raw materials, a medium-frequency induction furnace is adopted for smelting, and a carburant, silicon carbide, ferrocolumbium, nickel plates, ferrosilicon and ferrovanadium are added in different time phases of smelting, raw iron chemical components and smelting temperature expected by design can be achieved, and the product disclosed by the invention can be prepared through nodulization and two times of inoculation. By adopting the edium silicon molybdenum niobium spheroidal graphite cast iron material disclosed by the invention, an exhaust manifold of an engine can work under a working condition of about 800 DEG C, the high-temperature use property of the exhaust manifold can be improved, and the service life of the exhaust manifold can be prolonged.