Abstract: First of all, the in-loaded and out-loaded technologies of resonant cavity being used in the multi-beam klystron and some associated microwave attenuating materials are analyzed and compared. Not only the ways of adjustment of out-loaded resonant cavity quality characteristic is illuminated in theory, but is designed the out-loaded resonant cavity meeting the demand. Finally, the asymmetry of the E-field of the mode caused by the out-loaded cavity is adjusted and the influent factors and the change laws of quality characteristic of the out-loaded resonant cavity are located.