The invention discloses an intermediate N-Boc-3-aminopiperidine and a synthesizing method of optical isomer thereof. The prior synthesizing route has the disadvantages of high requirements on reactionconditions, high possibility of racemization, a great number of byproducts, as well as difficult post-treatment and difficult industrialization. The synthesizing method comprises the following steps:taking halogenated hydrocarbon as a solvent and organic alkali as an acid-binding agent, 3-piperidine ethyl formate is added with di-tert-butyl dicarbonate by dripping at temperature of 0-10 DEG C toobtain N-Boc-3-piperidine ethyl formate; 1,4-dioxane is used as a solvent, the N-Boc-3-piperidine ethyl formate undergoes ammonolysis reaction to obtain N-Boc-3-piperidine formamide; and the N-Boc-3-piperidine formamide is added by dripping in a solution with sodium hypochlorite and sodium hydroxide to obtain N-Boc-3-aminopiperidine. The invention has the advantages of no racemization during thereaction, high optical purity of the product, relatively moderate reaction conditions, simple operation, low total production cost, and easy large-scale industrial production.