The preparation method comprises the following steps that S1,
pig iron,
scrap steel and a crushed
alloy material are mixed, heated, kept warm and smelted, and molten iron is obtained; s2, a dam with the high middle and the two low sides is built at the bottom of the
ladle, a
rare earth magnesium-
silicon-iron
alloy nodulizing agent, a covering agent and a nucleating agent are sequentially laid on one side of the dam from bottom to top, the molten iron prepared in the S1 is flushed into the non-material-laying side firstly, and after the liquid level submerges the dam, the molten iron flows to the material-laying side to initiate a reaction; s3, molten iron obtained after the spheroidizing reaction and the
inoculation reaction are completed is subjected to heat preservation pouring; s4, after pouring is finished, a blank obtained in S3 is put into an annealing furnace, heat preservation is conducted, after furnace cooling is conducted, the blank is discharged out of the furnace and
air cooling is conducted, and the high-density spheroidal
graphite cast iron is obtained; the high-density spheroidal
graphite cast iron comprises the following components in percentage by
mass: 3.50-3.70% of C, 2.10-2.50% of Si, 1t of Mn and the balance of Fe. 0.30%, Slt; 0.10%, Plt; 0.06%, 0.10-0.20% of Cr, and 1t of Ni; 0.10% of Mo, 0.30-0.40% of Mo, and V: lt; 0.05%, Ti: lt; 0.08% of Cu, 0.30-0.40% of Cu, and the balance Fe and inevitable impurities.