Abstract: The density of nNaF·AlF3-Al2O3- CaF2-ZrO2 molten salt system with different molar ratio of NaF to AlF3 and ZrO2 contents was determined based on Archimedes law, and the effects of temperature and ZrO2 content were investigated. The results show that the density decreases with the increasing of temperature and the decreasing of molar ratio of NaF to AlF3. At 980°C, there is a good linear relationship between the density of 2.4NaF·AlF3-3wt%Al2O3- 3wt%CaF2 molten salt system and the ZrO2 content of 0~5wt%, which can be expressed as ρt(g·cm^-3) = 0.02844·w(ZrO2)+2.045 (r=0.9992). Within the present study range, the electrolyte density increases approximately by 0.02 g/cm³ with 1wt% ZrO2 addition.