Abstract: On the Basis of Khanh Nguyens multiple-beam FWG-TWT structure, the paper investigates the structure of 140 GHz multi-beam FWG-TWT, which can suppress the self-excited oscillation effectively. A lot of simulations have been done about the two-beam FWG-TWT. In comparison with one-beam model, the two-beam model can achieve higher power gain while the length is reduced and the self-excited oscillation is inhibited effectively.