The present invention provides a benzo[b,e]azepine compound based on an isatin skeleton, and the unique skeleton structure of the benzo[b,e]azepine compound has good antibacterial activity. A preparation method of benzo[b,e]azepine by a Lewis acid-catalyzed pyrrolidine ring-expansion synthesis process is also developed. The synthesis of polycyclic amines with complex structures is carried out by one-step method by use of 4-pyrrolidine isatin and various phenol compounds as substrates, and synthesis strategies of the polycyclic amines from pyrrolidine are extended. The synthetic method of the benzo[b,e]azepine compound has the advantages of convenient and easy-to-obtain substrate, convenient operation, high reaction activity, complete conversion of raw materials, and green economy.