The invention provides vermicular graphite cast iron resistant to seawater corrosion and a preparation method thereof. The vermicular graphite cast iron resistant to seawater corrosion comprises, by weight, 3.5%-3.7% of C, 2.8%-3.0% of Si, 0.001%-0.3% of Mn, 0.001%-0.035% of P, 0.001%-0.02% of S, 2%-3% of Ni, 0.3%-0.4% of Cu, 0.1%-0.2% of Mo, 0.2%-0.3% of Cr, 0.02%-0.03% of Sn, 0.003%-0.005% of Sb, 0.05%-0.10% of Ca, 0.1%-0.2% of Ti, 0.01%-0.02% of Zr, 0.01%-0.02% of Mg, 0.01%-0.02% of rare earth elements, and the balance Fe and inevitable impurities. The vermicular graphite cast iron is resistant to seawater corrosion, good in casting process performance and particularly suitable for casting critical components such as cylinder covers of marine diesel engines and has the advantage of lowproduction cost.