Abstract: Slag skin formed in electroslag remelting (ESR) is obviously deposited in layers in the thickness direction. In this pa-per, the specimens of slag skin in the production process were taken for experiment and analysis. The detailed microstructure and chemical composition were obtained at different positions. Based on the mechanism of quenching layer formation, it is suggested that the composition of the quenching layer can be used to reflect the composition of the slag pool in the corresponding time. The composi-tion change of the slag pool in ESR process can be speculated by checking the slag skin quenching layer near the mold at different posi-tions (different heights of an ingot).