Abstract: In order to improve the welding efficiency of thick wall pipe and the corrosion resisting property of the weld joint, narrow gap hot wire TIG welding was adopted for TP321 steel pipe with the size of φ406 mm×30 mm by all position automatic welding. The narrow gap groove parameters and the main welding parameters matching were studied. Welding tests were carried out according to different area with various parameters. The result shows that the good backing weld forming was obtained when the groove gap is 1 mm, thickness of the root face is 2.5 mm, and the width of the groove bottom is 9~10 mm. No defect was detected when the groove angles was 4°~5°. The weld current of down vertical position welding should be larger than that of downward welding, which was reverse when up vertical position welding. The weld heat input of the over head position welding should be increased appropriately compared with that of downward welding. The good weld appearance was obtained by wall position welding by using parameters above. And the RT inspection result shows that the welding quality is excellent.