A high-power YAG laser welding machine was used to seal the back end of the high performance third generation image tube (4J34 kovar alloy) and the fluorescent screen ring (4J49 kovar alloy). The effects of laser power and pulse width on welding joint forming and surface thermal diffusion were studied. The results show that the surface forming quality of 4J34 alloy and 4J49 alloy is the best when the maximum operating current is 100 A, the laser power is 195 W and the pulse width is 1.7 ms. Compared with the laser power, the pulse width has a more significant effect on the weld width and weld depth. The hardening in the welding center is the most serious, and the hardness is the lagest, followed by the heat affected zone.