This invention relates to the field of preparation methods for coaxial nanocables, specifically for silicon carbide/silicon dioxide (core/cladding) coaxial nanocables. The preparation method for silicon carbide/silicon dioxide (core/cladding) coaxial nanocables in this invention is as follows: place silicone oil, silicone grease, or siloxane in an alumina crucible or alumina boat, place the alumina crucible or alumina boat on a high-temperature resistant plate, then push the high-temperature resistant plate into a high-temperature furnace, evacuate the oxygen in the furnace, and introduce an inert gas for protection at a rate of 6-15 sccm, and raise the furnace temperature to 1000-1100°C at a rate of 5-15°C/min, then maintain the temperature for 1-5 hours before naturally cooling to room temperature. The products generated using the method described in this invention are all silicon carbide/silicon dioxide (core/cladding) coaxial nanocables. And the length is increased by two orders of magnitude compared to the existing methods, making it the longest nanocable reported so far. The preparation method is simple, the raw materials are cheap and readily available, the equipment requirements are simplified, the cost is low, and the yield is high.