Abstract: In order to study the effect of slag components on rare earth La in GH2984 superalloy containing rare earth La during electroslag remelting, a thermodynamic model for calculating the mass action concentration (activity) of CaF₂-CaO- Al₂O₃-MgO-TiO₂-La₂O₃ was established based on the ion-molecule coexistence theory(IMCT), and the experimental verification was carried out. The results show that La in the alloy can react with Al₂O₃ and TiO₂ in the slag at 1500 ℃-1700 ℃, and the lower the temperature, the greater the burning loss of La. With increase of the content of CaF₂, Al₂O₃ and TiO₂ in the slag, the activity of La₂O₃ decreases, and the burning loss of La in the alloy increases. With the increase of the content of CaO, La₂O₃ and MgO in the slag, the activity of La₂O₃ increases, and the burning loss of La decreases. With the content of Al₂O₃ in the slag increase from 18.37wt% to 24.76wt%, and the yield of La in the alloy decreases from 18.4% to 12.2%. With the content of La₂O₃ in the slag increases from 4.28wt% to 10.49wt%, and the yield of La in the alloy increases from 12.2% to 23.0%.