The invention relates to a magnesium-neodymium intermediate alloy and a preparation method thereof, and belongs to the technical field of metal materials and metallurgy. The magnesium-neodymium intermediate alloy comprises the following raw materials including, by weight, 10-15 parts of magnesium powder, 10-15 parts of neodymium powder and 0.1-0.15 part of a multi-element refining agent. The magnesium powder is added into a smelting furnace, a protective flux is added, slagging-off is conducted, the neodymium powder is added after slagging-off, the temperature is increased to 1050 DEG C after complete adding, the multi-element refining agent is added, the protective flux is added again after the temperature is increased to 1100 DEG C, secondary slagging-off is conducted, and a smelting material is prepared; brewing and boiling are carried out; ingot casting is carried out; testing is carried out; and carbon powder can serve as a pore-forming agent to decompose and release gas, on one hand, part of hydrogen in molten metal is taken away, on the other hand, nano-calcium-based powder is sintered at the temperature, a large number of porous structures are generated, the specific surface area of the nano-calcium-based powder is increased, the excellent adsorption performance is achieved, residual hydrogen and impurities in melt can be adsorbed, and the effects of refining and impurity removal are achieved.