Abstract: The surface tension of the LiF-CaF₂-Yb₂O₃ molten salt system is one of the key physical and chemical properties to optimize the preparation of Ni-Yb alloys by electrolysis. In this paper, the surface tension of the LiF-CaF₂-Yb₂O₃ system was measured by the pulling cylinder method in the temperature range of 1 173 K to 1 523 K, its changing laws were analyzed, and the surface tension of the Ni-Yb alloy was estimated. The results showed that the surface tension of the LiF-CaF₂ system decreased linearly with the increase of temperature in the range of 1 173 K to 1 573 K. The surface tension of the LiF-CaF₂-Yb₂O₃ system also decreased with the increase of temperature in the range of 1 173 K to 1 573 K, while the surface tension of the LiF-CaF₂-Yb₂O₃ system increased at first and then decreased with the increase of Yb₂O₃ concentration in the range of 1% to 4% (mass fraction). The surface tension of the LiF-CaF₂-Yb₂O₃ system reached the highest value when the content of Yb₂O₃ was about 1% (mass fraction) in the LiF-CaF₂ system. The surface tension of the liquid Yb-Ni alloy changed little with different components and temperatures. When the content of Yb is in the range of 0 to 0.10% (mole fraction), the surface tension of the Ni-Yb alloy is higher, so liquid Ni-Yb alloy easily separates from LiF-YbF₃-Yb₂O₃ molten salt.