Abstract: A Ku band gyro traveling wave tube (gyro-TWT) is designed in this paper. First, the design of the mag netic injection guns(MIG) is given. Second, it uses the dielectric loaded structure, which decreases the start current and in creases the start length in the tube. Finally, the linear polarized input coupler is designed. The gyro TWT is operated in 70kV, 10A, and the output peak power is 210kW, the gain is 35dB, 3dB bandwidth is 1. 8GHz.