Abstract: An efficient method for the synthesis of dihydroflavones from 2'−hydroxychalcones with polyphosphoric acid (PPA)/concentrated hydrochloric acid system using ethanol as solvent was reported. Synthesis conditions of compound a were optimized. Effects of reaction time, volume ratio of concentrated hydrochloric acid to ethanol and PPA equivalent on the yield were investigated. The optimum conditions for the synthesis of compound a are obtained: when reactant was 30.0 mg(0.1 mmol), the amount of PPA was 6.0 mmol, V(concentrated hydrochloric acid)/V(ethanol) was 1/1, the reflux reaction time was 3 h under the protection of nitrogen. Five products( a − f ) were synthesised in yields of 90.2%~93.6%, and were confirmed by MS, ¹H NMR and ¹³C NMR. The method has the advantages such as mild reaction conditions, short reaction time and excellent yield.