The invention relates to a steelmaking method which does not require an external heating source and mainly uses liquid pig iron as a raw material. Its main feature is that the physical heat of the liquid pig iron in the converter and the components in the pig iron, such as carbon, manganese, silicon, phosphorus and the like, are generated by the chemical reaction of oxygen sent into the furnace as a smelting heat source for steelmaking. In addition to molten iron, the charge also contains slag-forming materials (lime, quartz, fluorite, etc.); in order to adjust the temperature, scrap steel and a small amount of cold pig iron and ore can be added.