In this article, the interaction circuit, electron gun, and collector of a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ku</i> -band helix space traveling-wave tube (TWT) are optimized by using the multiobjective optimization design tools, which were developed by combining the nondominated sorting genetic algorithm II (NSGA-II) with the microwave tube simulator suite (MTSS). A prototype of the optimized TWT was then fabricated and tested at a beam voltage of 7.12 kV and a beam current of 90.14 mA. The testing results show that this tube is capable of providing over 200-W output power, over 54-dB gain, and over 69% overall efficiency within a 1-GHz bandwidth at the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ku</i> -band, with a good linearity performance. The optimization design process takes 49 h with the help of optimization design tools.