NOVELTY - Preparing monomer catechin from tea processing leftovers, comprises e.g. taking and crushing fresh tea leaves, adding water with the crushed leaves to carry out enzymolysis, adding cellulase, protease and pectinase complex enzyme into the mixture, filtering the mixed liquid and extracting the liquid using bi-acid ester and then drying, adding water into the extracted liquid, adding calcium chloride and zinc chloride mixed precipitator into the liquid, and filtering the liquid, dissolving the precipitate in dilute hydrochloric acid and filtering the precipitate.    USE - The monomer catechin is useful in a food processing, a health care medicine industry and a chemical industry.    ADVANTAGE - The method provides monomer catechin with high quality, high purity, high yield and good physiological activity in a simple, cost-effective and environment-friendly manner.    DETAILED DESCRIPTION - Preparing monomer catechin from tea processing leftovers, comprises: (a) taking and crushing fresh tea leaves; (b) adding water with the crushed leaves to carry out enzymolysis; (c) adding cellulase, protease and pectinase complex enzyme into the enzymolyzed mixture under an acidic condition, filtering the mixed liquid after enzymolysis reaction is completed, and extracting the liquid using bi-acid ester and then drying to obtain a tea polyphenol crude product; (d) adding water into the extracted liquid, adjusting a pH value of the liquid to be 5.6-6.5, adding calcium chloride and zinc chloride mixed precipitator into the liquid, and filtering the liquid to obtain precipitate; (e) dissolving the precipitate in dilute hydrochloric acid, filtering the precipitate using macro-porous absorption resin, and then washing with water, eluting precipitate using alcohol, concentrating and/or drying the eluate to obtain refined tea polyphenols; (f) adding water into refined tea polyphenols and then absorbing by macroporous resin adsorption, washing the mixture and eluting using bi-alcohol-water solution, and collecting epigallocatechin gallate, gallocatechingallate and epicatechin gallate eluent with a purity of 98%; (g) adding water with the eluent to make the bi-alcohol concentration of the eluting liquid to 10%, and (h) decompressing and concentrating the mixture using 90-99.5% of ethanol elution, and freezing and drying the concentrated mixture.    DESCRIPTION OF DRAWING(S) - The figure shows a flow diagram of a method for preparing monomer catechin from tea processing leftovers.