The structure, vaporization behavior and crystallization of CaF 2 –CaO–Al 2 O 3 slags with different SiO 2 contents for electroslag remelting were investigated by employing the TG and DSC measurements in conjunction with the Raman spectroscopy measurement for linking the macroscopic physicochemical property and microstructure information. The results show that SiO 2 addition makes the depolymerized aluminate units polymerized into fully polymerized Q Al 4 unit and Al–O–Al complex structural groups. With the SiO 2 content increasing to 6.1 mass%, the vaporization rate of fluoride increases because the SiF 4 possessing higher vapor pressure is formed and the SiO 2 addition can promote the formation of AlF 3 . As SiO 2 content is further increased to 8.6 mass%, the vaporization rate of fluoride decreases because the mass transfer becomes slower. The more complex slag structure resulted from SiO 2 addition dramatically decreases the crystallization temperature of the primary crystalline phase and the size of crystalline particles in the solidified slag.