Abstract: Single-pass tungsten inert welding with TGS-56 filling wire was conducted on 100 mm thick S08-Ⅲ steel used for nuclear pressure vessel and the macrostructure of the cross section of the welded joints was examined to analyze the effect of different welding parameters on the geometry of the welded joint. The results show that d changed obviously with the welding current, the wire feed speed mainly affected the bead height and the welding speed had great effect on the welded joint geometry. Temper bead welding technology could be easily achieved by using smaller welding current and greater wire feed speed to make b+h larger than d. The difference between b+h and d did not vary significantly with the welding speed.