The invention belongs to the field of medicine intermediates and particularly relates to a method for preparing 4-cyanophenylalanine (I). The preparation method is characterized in that with 2-[(benzyloxycarbonyl) amino] diethyl malonate (II) as a raw material, carrying out substitution on cyano halogenated benzyl, and sequentially carrying out ester group hydrolysis, decarboxylation and debenzylation by hydrogen catalysis to obtain the 4-cyanophenylalanine (I). The preparation method has the advantages that raw material is easily obtained, operations are simple and convenient, reaction yield is high, cost is low, selectivity is good and the like.