The invention relates to an amorphous alvimopan and a preparation method thereof, and concretely provides a new method for preparing alvimopan amorphous powder. The method comprises the following steps: dissolving alvimopan in a water and alcohol mixed solvent to form a solution, and carrying out spray drying on the solution to obtain the amorphous powder. The amorphous powder obtained through the method has very good temperature and humidity stability, the residual solvent and the residual water reach quality requirements, and the amorphous powder also has the advantages of suitable preparation process and long-term storage.