The invention provides a plasma excitation-based method for restraining the separation of a boundary layer in an air inlet passageway, and relates to a method for restraining the separation of the boundary layer in the air inlet passageway of a scramjet engine to improve the performance of the air inlet passageway, which is designed for solving the problem of the separation of the boundary layer generated at an inlet of the air inlet passageway in the case of flying under non-designed mach number. The method comprises the following steps of: 1, plating a ceramic film on the inner surface of each of a first radial passageway, a second passageway, a third passageway and a horizontal through hole; 2, connecting an input end of the horizontal through hole with an outlet of a plasma generator; 3, arranging two external electrodes on the surface of a conical surface, and embedding two internal electrodes in the conical surface; 4, spraying the plasma generated by the plasma generator at the inlet to generate jet flow type plasma; and 5, accelerating the jet flow of the plasma under the actions of electric fields of the external electrodes and the internal electrodes, accelerating the flowing of the airflow of the boundary layer, and restraining the separation of the boundary layer. The method is used for restraining the separation of the boundary layer in the air inlet passageway of the scramjet engine.