Design, simulation and test of a Denisov quasi-optical mode converter, which convert a 96 GHz whispering-gallery mode into Gaussian beam, was introduced. Based on the mode coupling theory, the design method of Denisov launcher is shown. To meet the layout requirement for the 96GHz TE6,2 Denisov quasi-optical mode convertor, a Denisov launcher was optimized. The configuration of the launcher is 6.4 mm for input radius and 52 mm in length. The amplitude of current at the cut edges of the launcher wall decrease to 10% of the focused current in the center. The energy conversion efficiency of output quasi-Gaussian beam reached 96.51%. The tested output field of Denisov mode converter is obtained. The diameter of beam waist is 22.4 mm. The vector conversion efficiency is greater than 95%.