The invention discloses a semi-synthesis method of phenolic hydroxyl flavonoid compounds and an iodine recycling method, relating to two ways A and B and iodine recycling, wherein in the way A, flavone is easily dissolved in a pyridine solvent of ethylene glycol or glycerin, and with iodine as a dehydrogenating agent, flavone is generated by heating and dehydration; in the way B, flavanone or flavone is not dissolved in pyridine of alcohol, the complexing of trivalent aluminum and flavanone is adopted, the solubility of the complexing and dehydrogenation products is high in alcohol, flavone is separated from the aluminum complex by use of phosphoric acid and the like, and flavone insoluble in water is separated out and obtained by filtering. The method disclosed by the invention is a universal method for preparing flavonoid compounds through dehydrogenation of phenolic hydroxyl dihydro flavonoids, the dosage of the reagents such as pyridine and the like is very small, and the treatment is simple, so that the method is suitable for industrial production. Take the diosmin preparation using hesperidin as an example, compared with the existing documents and patents, in the method disclosed by the invention, the dosage of organic solvents such as pyridine and the like is the least, the treatment is the simplest, the yield is the highest, and the method is environment-friendly (iodides can be oxidized by hydrogen peroxide, the recycling process is simple, and the yield is relatively high), and industrial production is easy to realize.