The invention relates to the technical field of the preparation of organic intermediates, and concretely relates to a method for preparing a Crebinostat intermediate 7-hydrazino-N-hydroxy-7-aminoheptane. The method comprises the following steps: 1, amidating: preparing 7-hydrazino-7-heptahexanoate from dimethyl pimelate, hydrazine hydrate and an alkali; and 2, carrying out esterification and hydroxylamine substitution: acidifying the 7-hydrazino-7-heptahexanoate to obtain 7-hydrazino-7-heptahexanoic acid, esterifying the 7-hydrazino-7-heptahexanoic acid, and reacting the esterified 7-hydrazino-7-heptahexanoic acid with hydroxylamine hydrochloride to prepare the 7-hydrazino-N-hydroxy-7-aminoheptane. The method has the advantages of easily available raw materials, mild reaction conditions, simplicity and convenience in post-treatment, greenness and environmental protection, recycling of a solvent, convenience in pilot scale test, and high yield.