Abstract: In order to suppress oscillation and maintain stability in the development of W-band folded waveguide traveling wave tube, this paper presents the analysis of reflection, backward wave and band edge oscillations. Periodic step structure together with other design and fabrication research improvement was applied to increasing the oscillation threshold. The investigation on oscillation suppression for W-band folded waveguide was carried out by simulation and experiment. After the methods mentioned above were applied as the most important key technologies to improving the output power and broadening the bandwidth, the developed W-band folded waveguide traveling wave tube could maintain stability from possible oscillations and reach over 100 Woutputpower with 5 GHz bandwidth at 20% duty cycle.