Abstract: A dynamic mathematical model for determining carbon contents in a converters has been established and the experiment was carried out in a induction furnace with a capacity of 50kg.Results are as follows:Contiuous analysis of exhaust gas content in a furnace by mass-spectrometer is accurate and quick.Flowrate of exhaust gas is calculated with high precision.Carbon contents in molten steel is calculated by the mathematicial model with a tolerance from 0 to 0.055%,and the average error of 0.03% during the whole blow process.Splashing is one of the factors which affect the accuracy of model estimation.In a practical production,with a larger furnace capacity and better condition, precision of the carbon content estimation will be improved to a large extent.