This study applied an explicit method to the fast structural design of the slow wave circuit in a 0.14 THz folded waveguide traveling wave tube. To valid the primary design, cold-circuit properties, such as dispersion and interaction impedance, were calculated by using both theoretical method and electromagnetic software(CST MWS) simulation. Simulation results showed that, the dispersion curve was almost flat around 0.14 THz, and the interaction impedance was about 1 Ω. In order to satisfy high output power demand, some changes were made. Interactive simulation by CST Particle Studio was found that modified structure could achieve more than 1 W output power around 0.14 THz. Micro Electrical Discharge Machining(EDM) and Micro milling were used for manufacturing a couple of period of the structure, respectively. It is found that both methods could satisfy the size accuracy, however, micro milling could obtain flatter surface and better surface roughness at the bottom.