Abstract: In this paper, the phenomena of beam-wave interaction in TWT with twisted twin comb slow-wave structure are investigated by particle-in-cell code in CST Particle Studio. The pictures of the track of electron beam along the z-axis are observed. Then, the output power, affected by four important electrical parameters including voltage, current, magnetic field and input power, is discussed. The results can be used to design the circularly polarized traveling-wave tube.