Abstract: Briefly described here in the essay is the structure of the internally-welding unit of the SAWH pipe two-step(pre-welding and finish welding)operation line.And elaborated are the one-key type arcing process and principle of the internally-welding function of the digital welding system.Also analyzed are the SAW arc self-adjustment process, and elements that may affect arcing stability of internally-welding operation, based on which, measures aiming at improving the arcing stability are determined, and taken.Relevant practice shows that the arcing stability of the internally-welding process is obviously improved, and so is quality of the SAWH pipe due to implementing such measures as optimizing parameters of the digital welder, setting the maximum wire-feeding speed, and taking the actual operation experience into consideration, etc.