Abstract: This paper introduces the thermal simulation analysis and optimization design method of the miniaturized traveling wave tube (TWT) amplifier. Firstly, the thermal loss of TWT is analyzed. Then, based on the thermodynamic theory and ANSYS Icepak software, the TWT amplifier is modeled and simulated. According to the characteristics of the miniaturized TWT, the thermal optimization design of the water-cooled plate and the slow-wave structure are carried out respectively. On this basis, the comprehensive optimization design of the water-cooled plate and the slow-wave structure is carried out. Finally, the experimental verification is excuted. The experimental results are in agreement with the simulation results. The overall and local temperature distribution characteristics of the TWT amplifier have been significantly improved.