Abstract: In order to study the influence of arc behavior on side wall heat input in narrow gap P-GMAW（pulsed gas metal arc welding） process, the arc behavior variation of welding torch at different distance from side wall was analyzed.Based on the double ellipsoid model, a heat source model considering arc motion and deflection was established by means of coordinate transformation, and the variation law of welding temperature field was obtained. It is found that when the distance between the welding torch and the side wall increases, the combustion position of the arc gradually transitions from the side wall to the bottom of the groove. The arc changes on the side wall according to the pulse frequency: the arc acts on the side wall position in the current base value stage, and the arc acts on the bottom of the groove in the peak stage. The temperature field results show that when the torch is about 1.5 mm away from the side wall, the weld seam is well formed. The improved heat source model can accurately describe the heat input of arc to the side wall when the torch is at different positions away from the side wall. The heat source model considering arc behavior can obtain more accurate temperature field distribution.