The invention discloses a preparation method of N-(pyrazine-2-radical carbonyl)-L-phenyl alanine. The preparation method comprises the following steps of: (1) making thionyl chloride react with pyrazine-2-formic acid in an organic solvent to obtain pyrazine-2-formyl chloride; (2) making thionyl chloride react with L-phenyl alanine in methanol to obtain L-phenyl alanine methyl ester hydrochloride;(3) dissolving pyrazine-2-formyl chloride and a metal M in tetrahydrofuran and adding the solution into a tetrahydrofuran solution of the L-phenyl alanine methyl ester hydrochloride and the metal M to obtain N-(pyrazine-2-radical carbonyl)-L-phenyl alanine methyl ester; and (4) dissolving the N-(pyrazine-2-radical carbonyl)-L-phenyl alanine methyl ester in an organic solvent and hydrolyzing underan alkaline condition to obtain N-(pyrazine-2-radical carbonyl)-L-phenyl alanine. A synthetic method has the advantages of less operation steps, high yield, readily-available raw materials and low environmental pollution, and is suitable for industrial production.