Abstract:As micro-vacuum electron devices based on Micro-Electro-Mechanical Systems(MEMS) technology for terahertz radiation sources, Folded Waveguide Traveling-Wave Tube(FWG-TWT) amplifiers have such characteristics as compact structure, great bandwidth, high power and etc. According to 345 GHz vacuum micro-electronic folded waveguide slow wave structure, its theory and design method are studied. Preliminary structure parameters are firstly determined by the linearity analysis theory, and then the model is simulated in 3-D PIC software, and the structure sizes are optimized. The relations between TWT gain and electrical parameters, geometry parameters, magnetic parameters are studied, which is helpful for the design of folded waveguides slow wave structure.