Abstract: The density of the aluminum electrolyte system where NaCl was used as an additive to substitute partly for LiF was studied. The electrolytic density was measured by an electronic balance connected to computer port according to the Archimedian law with an error less than 1%. Then, the measured electrolytic densities of Na3AlF6-AlF3 (10.87%-16.67%)-Al2O3-CaF2-LiF (0-6%)-NaCl (0-6%) system were analyzed through a 4-factor/4-level orthogonal experiment to develop a mathematical model based on those experimental results, i.e. ρt (g · cm^-3) = 2.8971-0.003 07AlF3 (w/%) + 0.003041LiF (w/%)-0.00932NaCl (w/%)-0.00085t (°C). The effects of cryolite ratio and LiF and NaCl concentrations on the densities were investigated. The results showed that the addition of NaCl decreases the density of aluminum electrolyte while the addition of LiF increases that of acidic electrolyte, but mixing the two additives properly may get excellent result. The more the NaCl used to substitute for LiF, the lower the electrolytic density.