Gallic acid has many uses in pharmacy, ink, dye, food, light industry and organic synthesis. Gallic acid and ferric ion form blue black precipitate, which is the raw material of blue black ink; It is also used in leather industry; It can also be used as photographic developer. Propyl gallate as antioxidant can be used in edible oil to prevent odor deterioration. In medicine, gallic acid is a hemostatic astringent and a local stimulant of mild chemical book. Application: it has antibacterial effect and can treat bacillary dysentery. It has the functions of astringency, hemostasis and antidiarrhea. It can be used as preservative. It can prepare pyrogallic acid, medicine, ink, mordant dye and explosion-proof agent. It is also used as a developer and analytical reagent for the detection of free inorganic acids, dihydroxyacetone, alkaloids and metals. It can be used as preservative, medium dye and explosion-proof agent.