A method for preparing an oxadiazacyclic compound , comprising: step 1: cyclizing compound with compound in the presence of a base to produce compound ; and step 2: reacting compound with a base to produce the oxadiazacyclic compound ; as shown in the following reaction scheme: wherein in step 2 the base is selected from an alkali metal or alkaline earth metal hydroxide, carbonate and hydrogen-carbonate or a mixture thereof; a molar ratio of the base to compound is 3.0-4.5:1, a reaction solvent is an aromatic hydrocarbon; and a reaction temperature is 0-200°C; wherein: R 1 is a C 1 -C 6 alkyl group, a C 6 -C 12 aryl group, or a heteroaryl group containing one or two atoms selected from nitrogen, oxygen and sulfur; R 2 is hydrogen, a C 1 -C 6 alkyl group, a C 6 -C 12 aryl group, a heteroaryl group containing one or two atoms selected from nitrogen, oxygen and sulfur, a C 1 -C 6 alkoxy group, or a C 6 -C 12 aryloxy group; R 3 and R 4 each are independently hydrogen, a C 1 -C 6 alkyl group, a C 6 -C 12 aryl group, or a heteroaryl group containing one or two atoms selected from nitrogen, oxygen and sulfur; Y 1 and Y 2 each are independently a halogen, a C 1 -C 6 alkylsulfonyloxy group, or a C 6 -C 12 arylsulfonyloxy group; and m and n each are independently 1 or 2. step 1: cyclizing compound with compound in the presence of a base to produce compound ; and step 2: reacting compound with a base to produce the oxadiazacyclic compound ; as shown in the following reaction scheme: wherein in step 2 the base is selected from an alkali metal or alkaline earth metal hydroxide, carbonate and hydrogen-carbonate or a mixture thereof; a molar ratio of the base to compound is 3.0-4.5:1, a reaction solvent is an aromatic hydrocarbon; and a reaction temperature is 0-200°C; wherein: R 1 is a C 1 -C 6 alkyl group, a C 6 -C 12 aryl group, or a heteroaryl group containing one or two atoms selected from nitrogen, oxygen and sulfur; R 2 is hydrogen, a C 1 -C 6 alkyl group, a C 6 -C 12 aryl group, a heteroaryl group containing one or two atoms selected from nitrogen, oxygen and sulfur, a C 1 -C 6 alkoxy group, or a C 6 -C 12 aryloxy group; R 3 and R 4 each are independently hydrogen, a C 1 -C 6 alkyl group, a C 6 -C 12 aryl group, or a heteroaryl group containing one or two atoms selected from nitrogen, oxygen and sulfur; Y 1 and Y 2 each are independently a halogen, a C 1 -C 6 alkylsulfonyloxy group, or a C 6 -C 12 arylsulfonyloxy group; and m and n each are independently 1 or 2. R 1 is a C 1 -C 6 alkyl group, a C 6 -C 12 aryl group, or a heteroaryl group containing one or two atoms selected from nitrogen, oxygen and sulfur; R 2 is hydrogen, a C 1 -C 6 alkyl group, a C 6 -C 12 aryl group, a heteroaryl group containing one or two atoms selected from nitrogen, oxygen and sulfur, a C 1 -C 6 alkoxy group, or a C 6 -C 12 aryloxy group; R 3 and R 4 each are independently hydrogen, a C 1 -C 6 alkyl group, a C 6 -C 12 aryl group, or a heteroaryl group containing one or two atoms selected from nitrogen, oxygen and sulfur; Y 1 and Y 2 each are independently a halogen, a C 1 -C 6 alkylsulfonyloxy group, or a C 6 -C 12 arylsulfonyloxy group; and m and n each are independently 1 or 2. <EOS>