NOVELTY - Synthesizing aztreonam, comprises adding (2-amino thiazolyl-4-yl)-2-(tert-butyl oxycarbonyl)-isopropoxy iminodiacetic acid as a starting material in an organic solvent and then reacting by passing hydrogen chloride gas through the saturation, adding polar solvent into a reaction system, filtering the crystal to obtain filter cake and drying to obtain 2-(((Z)-1-(2-amino-4-thiazolyl)-2-chlorine-2-oxo ethylidene)amino)oxygen-2-methyl propionic acid hydrochloride, adding alkaline substance to the organic solvent and then reacting, and separating and purifying reaction liquid to obtain aztreonam.    USE - The method is useful for synthesizing aztreonam (claimed).    ADVANTAGE - The method avoids the damage to beta-lactam ring by strong acid, eliminates the residue of 2-mercaptobenzothiazole of the product, and synthesizes the aztreonam with high yield and purity (99%).    DETAILED DESCRIPTION - Synthesizing aztreonam, comprises adding (2-amino thiazolyl-4-yl)-2-(tert-butyl oxycarbonyl)-isopropoxy iminodiacetic acid as a starting material in an organic solvent A at -30 to 30 degrees C and then reacting for 1-10 hours by passing hydrogen chloride gas through the saturation at -30-30 degrees C, adding polar solvent B into a reaction system, stirring and separating out precipitated crystal, filtering the crystal to obtain filtrate A, drying the cake to obtain 2-(((Z)-1-(2-amino-4-thiazolyl)-2-chlorine-2-oxo ethylidene)amino)oxygen-2-methyl propionic acid hydrochloride containing solution of chloride triphenyl phosphine and bis(trichloromethyl)carbonic ester, where the mole ratio of (2-amino thiazolyl-4-yl)-2-(tert-butyl oxycarbonyl)-isopropoxy iminodiacetic acid and dichloro triphenyl phosphine 1:1-1.5, adding an alkaline substance to an organic solvent C and then reacting at -25 to 25 degrees C under 2-(((Z)-1-(2-amino-4-thiazolyl)-2-chlorine-2-oxo ethylidene)amino)oxygen-2-methyl propionic acid hydrochloride for 0.5-5 hours, and separating and purifying reaction liquid to obtain aztreonam.