Abstract: A scheme for designing the double-gap output cavity with two coupling apertures, as well as a method for calculating the external quality factor of the output cavity were proposed in this paper based on the equivalent-circuit theory. A double-gap output structure with single coupling aperture that satisfied the needs of the impedance-frequency characteristics was designed by using the CST-MWS code, and then a double-gap output structure with double coupling apertures was obtained, with the same geometrical size of the front-cavity and output-cavity. The impedance-frequency characteristic curve of the output cavity with double coupling apertures can be consistent with that of the cavity with single coupling aperture, by properly adjusting the geometrical size of the cavity and the coupling slot. The novel method used in this paper can provide a simple and effective way of designing the double-gap output cavity with two coupling apertures.