Abstract: The high reliability girth welding technology of 12 layers thin-wall bellows and nozzles applied in high flexible expansion joint under strong vibration, high temperature and high pressure was studied systematically. The influence of argon protection on the back, diameter of welding wire, position of reinforcing ring and clearance between bellows and nozzles on welding quality was mainly studied. The results showed that for argon are welding process of bellows and nozzles, 1.6 mm wire diameter, 105 A welding current, strengthening thimble position and corrugated pipe straight segment end at the same height, 0.5 mm clearance between corrugated pipe and joint pipe were selected as the optimal welding parameters, the optimal welding quality was achieved with 3.1 mm maximum depth and best microstructure of fusion zone.