Extraction of total flavonoids from red kidney bean was studied by combination method of microwave and light wave radiation without solvent. Heating the sample for 8 min with power 800W (microwave 55% and light wave 45%), the total flavonoids were extracted with ethyl alcohol.The extraction ratio of total flavonoids is 1.04%, that is close with that of corresponding conventional extraction process. This method had many merits, such as simple, rapid, low cost, etc. Extraction mechanism was investigated preliminarily with high magnification fluorescence microscope FM, IR. It indicated that improvement of extraction efficiency of secondary metabolite is possibly because that plant tissue cell structure was changed by microwave.