Abstract: 3,4–dimethoxybenzoic acid and 2-hydroxyl-4-methoxyacetophenone as the starting material, 7,3',4'-trihydroxylflavone were synthesized by acylation,esterification, Baker-Venkataraman rearrangement，cyclization and demethylation，the overall yield was 47.3%. Microwave irradiation was applied in cyclization which was the key step. Comparing with traditional heating method， the use of microwaves was found to significantly improve product yields and shorten the reaction time. The appropriate microwave reaction time was 15 min and the yield was 92.1%. HOAc/40%HBr being used as the catalyst, the demethylation was performed under the conditions of 110℃ for 36h. Finally, The structures of the compounds were confirmed by IR, 1HNMR and MS. This method is simple, eco-friendly, high selectivity and has a wide range of applications.