A process for preparing avibactam, comprising steps of a compound of formula II is subjected to condensation reaction with O-protecting hydroxylamine hydrochloride in solvent a and under the catalysis of base a to prepare a compound of formula III: where R in the compound of formula II is identical to R in the compound of formula III, which is one selected from the group consisting of methyl, ethyl, isopropyl, n-propyl, tert-butyl, n-butyl, isobutyl, or benzyl; PG in the compound of formula III is one selected from the group consisting of methoxymethyl, benzyloxymethyl, tert-butyldimethylsilyl, tert-butyldiphenylsilyl, triethylsilyl or triisopropylsilyl; the compound of formula III is subjected to reduction with a reducing agent in the presence of concentrated sulphuric acid and ethyl acetate and chiral resolution to obtain a compound of IV: where R and PG in the compound of the formula IV have the same meanings as R and PG in the compound of formula III; the compound of formula IV is hydrolyzed in the presence of base b and in solvent b to obtain a compound of formula V; where PG in the compound of the formula V has the same meaning as PG in the compound of formula IV; the compound of formula V is subjected to urea cyclization and acyl chlorination with phosgene, solid phosgene or diphosgene in the presence of base c and catalyst in solvent c, and then is subjected to amidation to obtain a compound of formula VI; where PG in the compound of the formula VI has the same meaning as PG in the compound of formula V; the compound of the formula VI is subjected to deprotection with a deprotection reagent, sulfation, and tetrabutylammonium salt formation under the catalysis of base d and in solvent d to obtain the compound of the formula VII; the compound of the formula VII is subjected to ion exchange to obtain avibactam. a compound of formula II is subjected to condensation reaction with O-protecting hydroxylamine hydrochloride in solvent a and under the catalysis of base a to prepare a compound of formula III: where R in the compound of formula II is identical to R in the compound of formula III, which is one selected from the group consisting of methyl, ethyl, isopropyl, n-propyl, tert-butyl, n-butyl, isobutyl, or benzyl; PG in the compound of formula III is one selected from the group consisting of methoxymethyl, benzyloxymethyl, tert-butyldimethylsilyl, tert-butyldiphenylsilyl, triethylsilyl or triisopropylsilyl; the compound of formula III is subjected to reduction with a reducing agent in the presence of concentrated sulphuric acid and ethyl acetate and chiral resolution to obtain a compound of IV: where R and PG in the compound of the formula IV have the same meanings as R and PG in the compound of formula III; the compound of formula IV is hydrolyzed in the presence of base b and in solvent b to obtain a compound of formula V; where PG in the compound of the formula V has the same meaning as PG in the compound of formula IV; the compound of formula V is subjected to urea cyclization and acyl chlorination with phosgene, solid phosgene or diphosgene in the presence of base c and catalyst in solvent c, and then is subjected to amidation to obtain a compound of formula VI; where PG in the compound of the formula VI has the same meaning as PG in the compound of formula V; the compound of the formula VI is subjected to deprotection with a deprotection reagent, sulfation, and tetrabutylammonium salt formation under the catalysis of base d and in solvent d to obtain the compound of the formula VII; the compound of the formula VII is subjected to ion exchange to obtain avibactam.