A transient coupled mathematical model was established to study the oxygen transfer in electroslag remelting process. The electromagnetics, multiphase flow, heat transfer, mass transfer and species transport were simulated simultaneously with the aid of the finite volume method. The volume of fluid approach was employed to determine the interfaces among the slag, metal and air. An additionally kinetic and thermodynamic model was proposed to predict the mass transfer rates, which were related to the composition of each phase as well as the temperature. A laboratory experiment was carried out to validate the accuracy of the model. The increase of oxygen content in metal is primarily achieved during the formation of droplet, and the-mass transfer process at the slag/metal pool interface also contributes to it. The oxygen in air is absorbed into slag causing a rise in oxygen potential of slag, which significantly affects the oxygen content in metal. With the increasing content of ferrous oxide in slag, the mass fraction of oxygen in the metal pool first increases and then flattens out with time. The maximum calculated oxygen content in the metal pool is about 123.52 ppm during the ESR process. (C) 2017 Elsevier Ltd. All rights reserved.