Abstract: Provided is a method for preparing an oxadiazazole compound and/or a tautomer thereof, comprising: (a), in a solvent, in the presence of a dehydrating agent and a base, subjecting a compound as represented by formula 18 and/or a tautomer thereof to a ring-closing reaction to obtain a compound as represented by formula 19 and/or a tautomer thereof; and/or (b), in a solvent, under acidic conditions, subjecting the compound as represented by formula 19 to a tautomerization reaction as shown to obtain a tautomer thereof, such as a compound as represented by formula 20. The method for preparing the ?-lactamase inhibitor and the intermediate has a low cost, improves the repeatability and the scalability of key reactions, significantly increases the total yield and reduces the number of reaction steps as compared with the prior art, has the technical advantages of being green, safe, efficient and simple and convenient.