Abstract: Up and down narrow gap groove was separately studied. The results showed that,dowm sidewall fusion behavior: has the most obviously effects on down sidewall penetration depth, when the position of Tungsten electrode is between -1.5 mm and -2.5 mm, and weld is relatively stable;the welding current also has a greater effect on down sidewall penetration depth,when the base current is between 150 A and 250 A,there is a good fusion, the wire feed speed and pulse frequency have a greater influence on the weld surface bending degree and angle α. When the wire feed speed is increasing to 3 000 mm/min, the angle α is close to the right angle; When the pulse frequency is greater than 10 Hz, the weld surface has a very small degree of curvature,and the angle α is close to the right angle, the above two cases seriously affect the up sidewall fusion.Up sidewall fusion behavior: the position of Tungsten electrode and the arc voltage effects on up sidewall fusion behavior obviously, when arc voltage is 16 V and the position of Tungsten electrode is 1.5 mm,the up sidewall begins to be appearance of undercut. wire feed speed is greater than 3 000 mm/min, bad welds and on the side wall of fusion.