<p>The viscosity of 50% CaF₂-CaO-Al₂O₃-3% MgO slag systems with different TiO₂ or ZrO₂ was determined by using a high-temperature physical property tester, and the structure of the slag was analyzed by Raman spectroscopy. The results show that increasing both titanium oxide and zirconium oxide increases the viscosity of the slag system. Whereas the activation energy decreases and then increases with the increase of titanium oxide, the activation energy continues to decrease with the increase of zirconium oxide. This is primarily because both TiO₂ and ZrO₂ promote the transition from Q3 to the more complex Q4 unit. The increase in the number of non-bridging oxygen bonds (Al-O_nb) by Ca, Ti and Zr complex oxides also provides the impetus. The activation energy depends mainly on the amount of [Ti₂O₆]⁴⁻ in the slag. In addition, when the ZrO₂ content in the slag is increased from 6% to 8%, Zr-O stretching bonds and [c-ZrO₂] Zr-O stretching vibrational bonds are generated in the slag from CaZrO₃. This further increases the polymerization of the slag and forces the viscosity to increase. The results of the study can provide a theoretical basis for the related slag mobility in electroslag remelting.</p>