The present invention discloses a new flavanthrone synthesis method belonging to the technical field of dye processing. The method is improved on the basis of a traditional process, and comprises six steps, in a condensation step, low-boiling dimethyl formamide is used, and recovery cost is reduced; an anhydrous ferric chloride and copper powder compound catalyst is used to improve reaction efficiency, and in addition, sodium chlorate and hydrochloric acid are used for removing copper, copper removing effect is good, and product competitiveness is enhanced.