Abstract: An accelerating tube is described in this thesis. It is a part of an accelerator used for inspection of vehicle cargoes in rail cars, trucks, shipping containers, or airplanes in customs. A klystron with power of 4 MW and frequency of 2 856 MHz will be applied to supply microwave power. The electrons can be accelerated by a travelling wave in the accelerating tube about 220 cm long, with a buncher whose capture efficiency is more than 80 %. Energy of electrons after travelling through the tube can reach 9 MeV (pulse current intensity 170 mA)or 6 MeV (pulse current intensity 300 mA). Physical design of the accelerating tube, including the calculations of longitudinal particle dynamics, structure parameter and working character is carried out.