The invention relates to a preparation method of 3-amino-4-alkoxyimino piperidine. More particularly, the preparation method provided by the invention comprises the following steps: performing nucleophilic addition reaction on ethyl 3-aminopropionate hydrochloride and acrylonitrile in the presence of alkali; treating with di-tert-butyl dicarbonate to obtain ethyl N-tert-butoxycarbonyl-3-(2-cyanoethyl)aminopropionate; performing cyclization in the presence of strong alkali to obtain 1-N-tert-butoxycarbonyl-3-cyano-4-piperidone, and performing oximation to obtain 1-N-tert-butoxycarbonyl-3-cyano-4-alkoxyimino piperidine; sequentially performing cyano hydrolysis and Hofmann degradation reaction on the latter to obtain 1-N-tert-butoxycarbonyl-3-amino-4-alkoxyimino piperidine; and finally, performing deprotection to obtain the 3-amino-4-alkoxyimino piperidine and salt thereof.