Based on the research of 0.34 THz folded waveguide Traveling Wave Tube(TWT), dispersion characteristic, coupling impedance, loss characteristic and operating mode are analyzed. And electron optics system is designed for the 0.34 THz folded waveguide TWT. Test result of electron beam pass ratio greater than 80% is obtained by the beam practice experiment. The input and output structure optimal design is accomplished, and design indexes of the 0.345 THz folded waveguide are achieved for frequency band greater than 10 GHz and output power greater than 20 mW.