The invention relates to a method for preparing praseodymium-neodymium fluoride from praseodymium-neodymium oxalate. In the provided preparation method, praseodymium-neodymium oxalate directly reacts with HF gas at a temperature of 200 to 350 DEG C to generate praseodymium-neodymium fluoride, acidic water, and CO2, and anhydrous praseodymium-neodymium fluoride is produced. The provided preparation method has the advantages that the step that praseodymium-neodymium oxalate is burned into oxides at a high temperature is eliminated, the problem that a large amount of waste acid is discharged is solved, the cost is reduced, the cost for each ton can be reduced by 2000 yuan, and the industrial promotion prospect is wide.