Abstract: A novel slow-wave structure, folded rectangular groove waveguide, suitable for E-band space traveling wave tube is analyzed in this paper. It derives from the idea of bending a conventional rectangular groove waveguide along its longitudinal direction. Electromagnetic simulation software Ansoft HFSS is used to design and optimize the critical geometry size of E-band folded rectangular groove waveguide, to simulate the trend of interaction impedance along the x and y directions at center frequency of 83.5 GHz, and to conclude the fact that higher average interaction impedance can be achieved by applying the sheet electron beam. According to the simulation with CST particle studio, the output power of folded rectangular groove waveguide traveling wave tube is 210 W, and the electron efficiency reaches 8.05% at the center frequency of 83.5 GHz.