NOVELTY - Synthesizing 7-amino-3-vinyl-3-cephem-4-carboxylic acid, comprises adding acetone and dimethylacetamide in a flask and then stirring and reacting, adding 7-phenylacetamide-3-chloromethyl-4-cephalosporanic acid p-methoxybenzyl ester and triphenylphosphine and then stirring and reacting, adding potassium iodide and formaldehyde and then stirring and reacting to obtain reaction mixture, extracting the reaction mixture with aqueous sulfuric acid, separating organic phase, adding dichloromethane and then heating and cooling, and filtering the cooled mixture and then washing and drying.    USE - The method is useful for synthesizing 7-amino-3-vinyl-3-cephem-4-carboxylic acid (claimed).    ADVANTAGE - The method is capable of economically synthesizing the 7-amino-3-vinyl-3-cephem-4-carboxylic acid with improved purity and high conversion rate in an eco-friendly manner.    DETAILED DESCRIPTION - Synthesizing 7-amino-3-vinyl-3-cephem-4-carboxylic acid, comprises adding acetone and dimethylacetamide in a reaction flask and then stirring and reacting, adding 7-phenylacetamide-3-chloromethyl-4-cephalosporanic acid p-methoxybenzyl ester and triphenylphosphine and then stirring and fully reacting, adding potassium iodide and 37% formaldehyde and then stirring at 10-12 degrees C for 1 hour and reacting, adding 1 mole/l of sodium hydroxide solution and then heating and reacting at 33-35 degrees C for 30 minutes to obtain reaction mixture, extracting the reaction mixture with aqueous sulfuric acid and then stirring to obtain extraction liquid, separating organic phase and then decompressing, adding dichloromethane and then heating for 30 minutes and cooling to temperature of 0-5 degrees C for 1 hour, filtering the cooled mixture and then washing and drying in a vacuum until moisture content is less than 0.5% to obtain 7-phenylacetamido-3-vinyl cephalosporanic acid-p-methoxybenzyl ester intermediate, adding the obtained intermediate with phenol in the reaction flask and then stirring for 3.5 hours and reacting at 48-50 degrees C, adding ethyl acetate and then stirring for 5 minutes and cooling to 10 degrees C, adding 5% of sodium hydroxide solution and then stirring and heating to 30-35 degrees C, adding immobilized penicillin acylase and then stirring at pH value of 5-5.5, performing hydrolysis reaction of the stirred mixture for 1 hour and then filtering, adding the filtrate with a certain amount of EDTA, sodium hydrosulfite and active carbon with hydrochloric acid solution and then stirring at temperature of 5 degrees C and pH value of 3.5-4, cooling, filtering and drying in a vacuum.