Abstract: To optimize the thermal and kinetic conditions for the preparation of Al-Cu-Y alloys by electrolysis, the variation law of density, viscosity and conductivity of AlF3-(Li, Na)F-(Al₂O₃-Y₂O₃) molten salt systems was studied. The change law of density, conductivity and viscosity with different oxide concentration contents in this system was measured by the Archimedes method, continuously varying conductivity cell constant method and rotation method when (Li, Na)F: AlF₃ (molar ratio)=2.5 in the temperature range of 900-1 000 ℃. The results showed that the density, viscosity and conductivity were linear with the fixed composition of Al₂O₃ and Y₂O₃ in such a temperature range. At a constant temperature of 950 ℃, the density of the molten salt system decreased linearly with increasing Al₂O₃ content and increased linearly with increasing Y₂O₃ content; with increasing oxide content (Al₂O₃ or Y₂O₃), the conductivity of the molten salt system decreased linearly, while the viscosity of the system increased linearly.