Abstract: A mathematical model of decarburization in EAF steelmaking was constructed to predict the variation of carbon content in the bath continuously and control the terminal point of carbon content on the basis of the technology of fume composition infrared detecting, calculations of mass balance and production data such as carbon amount and oxygen flow.The simulated results of production data form the 50 t UHP EAF in Special Steel Plant of Laiwu Iron and Steel Co.Ltd.indicate that this model achieves its aim to continuously predict and terminally control carbon content in the molten bath.It is also shown that the decarburization rate which can achieve 0.12% to 0.16% min^-1 is mainly influenced by oxygen flow rate.This model can be used for oxygen supply optimization to reduce oxygen consumption.