The invention discloses an alpha-cyanidation method of mono-alkyl substituted aniline. According to the method, various aromatic, aliphatic, and heterocycle substituted secondary amines of anilines are taken as the raw materials, trimethylsilyl cyanide is taken as the cyanidation agent, divalent iron is taken as the catalyst, tert-butyl hydroperoxide is taken as the oxidizing agent, raw materials carry out reactions in a solvent, and the reaction product is processed by a simple concentrating and purifying technology to obtain the finished product. The invention aims to solve the shortages of a conventional catalytic oxidation cyanidation method of secondary amines and provides a novel synthesis method. Cheap, low toxin, and easily available divalent iron is taken as the catalyst, tert-butyl hydroperoxide is taken as the oxidizing agent, and the catalytic oxidation cyanidation reactions between a secondary amine substrate of various aromatic, aliphatic, and heterocycle substituted anilines and trimethylsilyl cyanide are realized efficiently. The provided method has the advantages of simple technology, safe production reactions, easy operation, short reaction time, and easiness for industrialization.