To address the urgent needs of future high-capacity, high-rate communication systems for key Traveling-Wave-Tube(TWT) characteristics—high frequency, high power, and wide bandwidth—a new hybrid slow-wave structure that combines a helical slow-wave structure with a folded-waveguide slow-wave structure is proposed, aiming to realize broadband performance and thermal stability in TWTs. Through theoretical analysis and design simulations, the transfer relationships between electron-beam parameters and high-frequency parameters in the hybrid slow-wave system are studied, and beam-wave interaction simulations are conducted. Based on these studies, an E-band hybrid slow-wave structure TWT prototype is designed and fabricated; its output power and gain are tested, and the main parameters are compared with those of a conventional Folded-Waveguide(FWG) TWT. Test results show that the hybrid slow wave structure TWT delivers more than 78 W output power and more than 20 dB saturated gain over 68~80 GHz, while its in-band small-signal gain parameter is reduced by more than 50% relative to the folded-waveguide device, verifying the feasibility and effectiveness of the hybrid slow-wave structure.