This paper studied the changing principles of carbon content in direct reduction iron(DRI) and liquid iron in the COREX melting gasifier. Under the normal workingconditions of experimental equipment, liquid nitrogen was poured into the meltinggasifier from its tuyere to cool down quickly. And then seven cross sections were madeto study the carburization reaction and its characteristics of the solid iron and theliquid iron, and also the reaction of carbon between the slag and the metal. Accordingto the results, the influences of the thickness of the semi-coke layer and the temperatureon the carbon content of liquid iron in the COREX melting gasifier were confirmed.