The main components of a space helix TWT (traveling wave tube) are electron gun, helix slow-wave system and collector. Thermal issue is of great importance for space helix TWTs. High heat efficiency of cathode is required for electron gun, as well as high heat transmission capacity for slow-wave system and collector. Some structure optimization for the electron gun, slow-wave system and the collector of some type of space helix TWT has been proposed aiming the above purpose. To evaluate the structural optimization means, the related thermal analysis has been carried out using ANSYS software. The simulation results demonstrate that the structure optimization is effective. And the actual effect needs to be further studied.