Staggered double vane traveling wave tubes have been given a lot of attentions in recent years due to its high power capacity and easy double vane traveling wave tubefabrication. However, the loss seriously limits the performance of traveling wave tube with the increasing of frequency, especially in THz wave band. In this paper, a more practical design about staggered double vane structure is proposed with the consideration of the loss and fillets caused by fabrication. The simulation results indicate that the tube with uniform period slow wave structures can obtain over 5 W output power in the frequency range from 320 GHz to 342 GHz. The method of phase-velocity taper is used to enhance the output power and the simulation results show an obvious improvement of the power with more than 28% in the operating wave band. Based on these, the experiment of the fabricated high frequency system with filleted staggered double vane slow wave structure is carried out. The tested S21 of pillbox window is above -2.1 dB in the frequency range from 330 GHz to 360 GHz and VSWR (voltage standing wave ratio) is below 1.35 in the frequency range from 334 GHz to 355 GHz. And the tested VSWR of the high frequency system including the pillbox window is below 2 in the frequency range from 335 GHz to 344 GHz, which matches with the simulation results.