Abstract: The thermal deformation of gridded electron gun in traveling wave tube has much influence on the performance of its electronic optics system and the problem has been investigated by means of the coupling of the thermal field and the mechanics field based on FEM (infinite element method). The results show that the total deformation of the anode is maximum and reaches 0.28 mm and the deformation of control grid, shadow grid, cathode and some supporting structure is toward the anode. Besides, contact or cross of control grid and shadow grid doesnt occur due to their deformation caused by temperature rise, while the cathode will contact the shadow grid when the deformation of the cathode is larger. The above contact will affect the performance of the gun, even cause the damage to shadow grid. The deformation of the components can be lessened by means of lowering probability of electron interception, thickening control grid and shadow grid properly as well as adopting the material with higher thermal conductivity and lower coefficient of linear expansion.