Kinetics of slag-metal reactions was investigated in order to elucidate the mechanism of Al-oxidation and oxygen increase during industrial electroslag remelting (ESR) process. G20CrNi2Mo bearing steel was utilized as the consumable electrode and remelted using a 2400-kg industrial ESR furnace. It was found that with the content of FeO in the slag increasing from 0.20 wt% to 0.45 wt%, the content of oxygen increased from 12 ppm in electrode to 16 ppm, 21 ppm in the ingot while Al decreased from 0.040 wt% in the electrode to 0.031 wt%, 0.019 wt% in the ingot. Based on penetration and film theories, a kinetic model has been developed. The model indicates that Al in the electrode is mainly oxidized by FeO at the metal film. Increase of soluble oxygen mainly occurs during the time of droplet formation and falling. The content of soluble oxygen occupies about fifty percent of the total oxygen. The rate-determining step of Al-oxidation is the mass transfer of Al at metal side, whereas oxygen increase lies in the mass transfer of FeO at slag side. With the content of FeO increasing from 0.20 wt% to 0.45 wt%, the mass transfer resistance of FeO decreases obviously, thus would result in an increase of Al-oxidation and total oxygen. In order to improve the cleanliness of refined ingot, it is more effective to decrease the oxygen potential of slag pool to a minimum level, or decrease the time of droplet formation and the temperature of slag pool to some extent, rather than improve the Al content in the electrode.