Abstract: Using the geometrical optics theory, the working principle of high-order overmoded Denisov launcher is analyzed. Based on the mode coupling theory, the design method of the Denisov launcher is put forward. The TE6,2 Denisov launcher is studied using the concrete parameters of the 3 mm whispering-gallery mode gyrotron. By adopting developed mathematical programme, reliable optimal geometrical parameters of wall distortion are obtained. The 96.4 GHz TE6,2 Denisov launcher with compact structure is designed, and is verified by an electromagnetic field emulator. Results show that the launcher wall current is well focused,the current of cut edges decreases to 10% of the central focused current, and the power conversion efficiency of the output quasi-Gaussian bundle is 96.51%.