Preparation method of cylinder block for large ship

The invention provides a preparation method of a cylinder block for a large ship and belongs to the technical field of casting. Comprising the following steps that raw materials are prepared from 20 wt.% of common pig iron, 60 wt.% of high-manganese waste steel, 20 wt.% of foundry returns, ferrosilicon, ferromanganese, pure copper, tin, a carburant, ferrous sulfide and antimony; melting is conducted; a spectrum sample and a chemical sample are taken at the position 100 mm below the liquid level of the molten iron for chemical component analysis, and then according to chemical component setting, alloy is supplemented through component difference, so that the range of the microelements in the molten iron is as follows: Mn is larger than or equal to 0.8 wt% and smaller than or equal to 0.9 wt%, P is smaller than or equal to 0.1 wt%, S is larger than or equal to 0.06 wt% and smaller than or equal to 0.09 wt%, Cu is larger than or equal to 0.60 wt% and smaller than or equal to 0.65 wt%, Sn is larger than or equal