Abstract: A Ni—Al-RE ternary eutectic alloy and a preparation method thereof are provided. The alloy is composed of the following elements by weight percent, aluminum (Al) of 2.50% to 19.50%, rare earth (RE) of 1.30% to 20.0%, other impurity elements being less than or equal to 0.10%, and the rest being nickel (Ni). The microstructure of the alloy is in a completely eutectic form, and the density is 6.8 to 7.1 g/cm3. Raw materials are prepared according to the ratio, and are placed into a vacuum induction smelting furnace; the smelting furnace is vacuumized to 10?5 Pa, power is increased to ensure complete melting of the raw materials, and the molten alloy melt is poured into an iron mold to obtain alloy ingots. The eutectic phase in the microstructure of the alloy in the disclosure has high hardness.