Based on the development of the 0.14 THz, 0.22 THz, and 0.34 THz folded waveguide Traveling Wave Tubes(TWTs), the design and fabrication for 0.41 THz folded waveguide slow wave structure is discussed. The differences between circular bend and orthogonal bend affecting the dispersion, coupling impedance, loss, bandwidth, and gain of the 0.41 THz folded waveguide TWT are investigated. The effects of beam profile on dispersion, coupling impedance, loss, bandwidth, and gain of the 0.41 THz folded waveguide TWT are analyzed. The influence of sever on bandwidth and gain of the 0.41 THz folded waveguide TWT is presented. The initial design scheme for 0.41 THz folded waveguide TWT slow wave structure is obtained. This work can lay the foundation for developing THz folded waveguide TWTs.