The invention discloses a method for preparing a precursor for chemical vapor deposition of metallic rhenium and belongs to the technical field of material preparation. According to the method, ReCl5 is made to react in an oxidizing atmosphere, efficient solid-liquid-gas separation is conducted on reactants and products with a sand core filter bulb so that reactants, reaction products and waste gas can be effectively separated, the reaction products ReOCl4 and ReO3Cl are gathered in a collection vessel heated by an oil bath pan at the same time, oxygen introduction is stopped after reaction ends, circulation of inert gases is maintained, a tube furnace is cooled, the oil bath pan is heated at the same time to enable ReO3Cl to volatilize to enter a rectification unit to be collected, ReOCl4 is purified, and then the high-purity precursor ReOCl4 for chemical vapor deposition of metallic rhenium is obtained. By the adoption of the method, reaction efficiency is high, ReOCl4 and ReO3Cl are separated through rectification, and the purity of the product ReOCl4 is improved.