The invention relates to a preparation method of N-ethyl-3-phenylpropylamine, and belongs to a preparation method of a compound. The preparation method comprises the following steps: dropwise adding 3-hydrocinnamaldehyde into an alcohol solution of ethylamine hydrochloride to carry out reaction under protection of inert gas; putting metal borohydride into a reaction system to carry out reduction reaction after a reaction terminal is reached; controlling a temperature to -20 to 15 DEG C; slowly adding a quenching solution into the reaction system to stop reaction, and simultaneously hydrolyzingthe generated organic boride; carrying out separation and purification on the generated target compound N-ethyl-3-phenylpropylamine or corresponding salt of the N-ethyl-3-phenylpropylamine. The preparation method disclosed by the invention has the advantages that production of relevant tertiary amine and quaternary ammonium salt side-products is avoided, an influence of the reaction on an environment is reduced, and the method has the environmental protection advantage; the operation is safe, simple and convenient, a requirement on equipment and operation personnel is low; energy consumptionis little, the security is high, and the the method is suitable for industrialization; the yield is high, and the post-processing is simple and feasible.