Abstract: Three problems were studied for the coaxial output cavity operating at TM₄₁₀ mode for multiple-beam klystron, which were the higher external Q-factor, the worse field distribution symmetry, and the small frequency interval between operating mode TM₄₁₀ and neighboring modes. In order to resolve these problems, a coaxial output cavity with metallic rings and shorting bar is presented. Setting the shorting bar suitably can not only decrease external Q-factor, but also make field distribution uniform. Furthermore, inserting the metallic rings can enlarge frequency interval between operating mode and neighboring modes. This kind of coaxial output cavity in X-band operating at TM₄₁₀ mode was modeled and simulated by CST-MWS. The frequency interval between TM₄₁₀ mode and neighboring modes is enlarged to more than 1.3 GHz, the external Q-factor is diminished 42.7% (from 540.4 to 309.6), and the symmetry of the field distribution of TM₄₁₀ mode is improved.