The invention discloses a banded electron beam double-slot trapezoid line coupling cavity slow wave device, which is composed of a line coupling cavity body formed by alternately connecting a plurality of cavities and cavity walls. Each cavity wall is provided with a coupling slot close to and parallel to the narrow edge of the corresponding cavity and a coupling slot close to and parallel to thewide edge of the cavity, and a banded electron beam channel shaped like the coupling slot parallel to the wide edge is arranged at the center of each cavity. The electromagnetic wave transmitted alongeach cavity is coupled to the next cavity by the coupling slots. When an electron beam is injected into any banded electron beam channel, the electron beam interacts with the high-frequency field electromagnetic wave in the corresponding cavity for energy exchange, the high-frequency field electromagnetic wave modules the electron beam, and the modulated electron beam yields energy so as to amplify the electromagnetic wave.