Abstract: The present disclosure discloses a method for preparing lenalidomide. The present disclosure provides a method for preparing lenalidomide I, which comprises the following steps: in a solvent, the lenalidomide intermediate II is reduced with a metal in the presence of an organic acid to obtain the lenalidomide I, wherein the metal is one or more selected from zinc, iron, aluminum and manganese. The preparation method of the disclosure has simple and safe operation, simple post-processing steps, environmental friendliness, high total yield. Moreover, the product obtained in the method has a purity of more than 99.90%, maximum single impurity of less than 0.10%, total heavy metal residue of less than 10 ppm and meet the heavy metal residue standard and API standard. Furthermore, the method has a low production cost and is suitable for industrial production.