The invention discloses a preparation method of 2-azanoradamantane-N-Oxyl (Nor-AZADO). The method comprises the following steps: placing acetonedicarboxylic acid, glutaraldehyde and benzylamine in an aqueous hydrophosphate solution, and carrying out condensation and decondensation to obtain 9-benzyl-9-azabicyalo-[3,3,1]-nonyl-3-one; carrying out condensation dehydration on 9-benzyl-9-azabicyalo-[3,3,1]-nonyl-3-one and benzene or benzene ring substituted sulfohydrazide, and adding an alkali to obtain 2-(9-benzyl-9-azabicyalo-[3,3,1]-nonane-3-ylidene)-1-benzene or benzene ring substituted sulfohydrazide sodium/potassium salt; carrying out refluxing ring closing on the 2-(9-benzyl-9-azabicyalo-[3,3,1]-nonane-3-ylidene)-1-benzene or benzene ring substituted sulfohydrazide sodium/potassium salt in an organic solvent to obtain N-benzyl-2-azanoradamantane; debenzylating N-benzyl-2-azanoradamantane to obtain 2-azanoradamantane; and oxidizing 2-azanoradamantane by a peroxide oxidant to obtain the Nor-AZADO. The preparation method has the advantages of great increase of the synthesis yield, greenness and environmental protection, high efficiency, low cost, and easiness in industrial large-scale production.