What is provided in the present invention is a simple method for preparing Vaborbactam, in which S-3-hydroxy-6-oxohexanoic acid ester is used as the starting material to finally form the Vaborbactam (I) by carrying out the procedures of hydroxyl protection, imidization, asymmetric addition from borane or borate compounds, amino deprotection, amidation, cyclization and hydrolysis. The present invention is suitable for commercial production by virtue of the advantages: widely available and low cost raw materials; safe, simple and convenient process steps; no rigorous reaction conditions; and environment-friendly reaction courses.