Casting method of thick and large castings

The invention discloses a casting method of thick and large castings. Coke is used as fuel; metal furnace materials are smelted into smelted steel in a cupola furnace; tapped smelted steel, nucleating agent and electrolytic copper are flushed into a casting ladle; the fixed carbon content in the coke is above 87%, thereby the tapping temperature of the smelted steel in the copula furnace can be ensured to be above 1500 DEG C so as to obtain purified smelted steel; the nucleating agent contains 0.2%-0.5% of silicon-barium nucleating agent, 0.2%-0.4% of 75% ferro-silicon and 0.1%-10% of molybdenum-containing nucleating agent based on the weight of the tapped smelted steel; the silicon-barium nucleating agent and the 75% ferro-silicon have the action of increasing the crystallizing core of the graphite in the smelted steel; the graphite in the smelted steel is fine and is distributed uniformly so that the internal and external performances of thick and large castings are consistent; the electrolytic copper and t