NOVELTY - Flavonoid is prepared from dihydro flavonoid by carrying out pathway A i.e. preparing flavonoids through dehydrogenation of dihydro flavonoid by dissolving iodine, trivalent iron salt, dihydro flavonoid, and pyridine and its derivative in alcohol, heating, sealing, stirring to react to obtain ferrous salt and flavonoid, diluting with alcohol, adding acid in pyridine and its derivative, preserving heat in water bath, adding iron-removing agent, stirring until there is no iron complex color, uniformly stirring, preserving heat in water bath, filtering, and washing.    USE - Preparation of flavonoid from dihydro flavonoid for pharmaceuticals and chemicals.    ADVANTAGE - Preparation method is simple, easy, environment-friendly, and low in cost, has high product yield and purity, greatly reduces adding amount of iodine and pyridine, and reduces product cost.    DETAILED DESCRIPTION - Flavonoid is prepared from dihydro flavonoid by carrying out pathway A i.e. preparing flavonoids through dehydrogenation of dihydro flavonoid by dissolving iodine, trivalent iron salt, dihydro flavonoid, and pyridine and its derivative in alcohol, heating, sealing, stirring to react to obtain ferrous salt and flavonoid, diluting with alcohol, adding acid in pyridine and its derivative, preserving heat in water bath, adding iron-removing agent, stirring until there is no iron complex color, uniformly stirring, preserving heat in water bath, filtering, washing, placing filter cake in alcohol solution of phosphoric acid, and washing 2-3 times, or carrying out pathway B i.e. preparing flavone aglycone through dehydrogenation and hydrolysis desugarization of dihydro flavone glycoside by dissolving iodine, trivalent iron salt, dihydro flavonoid, and pyridine and its derivative in alcohol, heating, sealing, stirring to react to obtain ferrous salt and flavonoid, diluting with alcohol, adding organic base with amount of greater than or equal to 1 time of acid, adding hydrosulfite, placing in water bath at 40 degrees C, hydrolyzing, tracking non-glucoside using thin-layer chromatography (TLC)/HPLC, and filtering.