Abstract: The gyro-TWT is sensitive to the electronic beam (velocity ratio，velocity spread etc.), while the parameters were master key in the experiment. The hot cathode and high quality MIG （magnetic injection gun） plays an important role at stability and long life of Gyro-TWT.The MIG，cathode and hot filament were optimum designed, the MIG velocity spread was 2%,which was reported 3% in international documentations. By thermal analysis and deformation analysis, we improved the structure of cathode and preparation technology which increased obviously the efficiency of hot filament, the cathode power was debased from 100kW to 50kW, exaltated the uniformity and stability of cathode. These methods protected the life of cathode and GyroTWT. The utility model of MIG was assemblied in gyroTWT,then in the experiment the pulse power is more than 100kW, the average power was more than 10kW, the state of gyroTWT was stabilty and credibility during long time span. 