NOVELTY - Preparation of 7-amino-3-cephem-4-carboxylic acid (7-ANCA) comprises esterifying to penicillin G/K with diphenyl carbinol, oxidizing by peracetic acid, performing open loop and rearrangement to trimethyl phosphate, oxidizing by ozone, reducing trimethyl phosphate, esterifying with p-toluenesulfonylchloride, performing morpholine alkene amination, bromination, and hydrochloric acid cyclization, reducing flomoxef by sodium borohydride, performing esterification to methylsulfonylchloride, reacting with protective group with anhydrous aluminum chloride and enzyme.    USE - Method of preparation of 7-amino-3-cephem-4-carboxylic acid (7-ANCA) (claimed).    ADVANTAGE - The method utilizes low cost raw material, high yield, and is suitable for industrial production, has reduced extraction and treatment process, reduced using dosage of solvent and discharge quantity of wastewater, saves energy, and reduces environment pollution.    DETAILED DESCRIPTION - Preparation of 7-amino-3-cephem-4-carboxylic acid (7-ANCA) comprises:    (A) esterifying to penicillin G/K (compound 7) with diphenyl carbinol, oxidizing by peracetic acid, performing open loop and rearrangement to trimethyl phosphate to obtain thiazoline-nitrogen heterobutanone derivative (compound 32), and eliminating solvent in reaction;    (B) oxidizing compound 32 by ozone, reducing trimethyl phosphate to obtain enol ester (compound 33), eliminating solvent in reaction, esterifying to compound 33 with p-toluenesulfonylchloride, performing morpholine alkene amination, bromination, and hydrochloric acid cyclization to obtain flomoxef;and    (C) reducing flomoxef by sodium borohydride, performing esterification to methylsulfonylchloride, and diethylamine eliminating to obtain 7-ANCA (compound 35) with protective group, eliminating solvent in reaction, reacting compound 35 with protective group with anhydrous aluminum chloride, eliminating protective group of diphenyl carbinol to obtain 7-ANCA compound 36 with phenylacetyl group, reacting compound 36 with enzyme, eliminating phenylacetyl group, and preparing 7-ANCA.