Methods for producing a magnesium-rare earth intermediate alloy, which belongs to the technical field of molten salt electrolytic metallurgical technology. In one embodiment, the method comprises subjecting magnesium chloride, lanthanum praseodymium cerium chloride and potassium chloride to an electrolysis, and adding additional lanthanum praseodymium cerium chloride and magnesium chloride during the electrolysis. In the electrolysis process, neither metal magnesium nor rare earth metal is used, only the chlorides of rare earths and magnesium are used and the rare earth ions and the magnesium ions are co-electrodeposited on the cathode, so as to obtain the intermediate alloy having a melting point close to the eutectic temperature of the rare earth and magnesium. The method has various advantages including but not limited to high operability, simple process and equipment, stable quality of product by mass production and easy for commercial scale production.