Abstract: Gas Tungsten Arc Weld (GTAW), which was characterized as flexible operation, high welding quality, is widely used in critical welding production, especially in the backing welding of pressure pipelines, boilers and pressure Vessels. In the process of GTAW, the use of different welding methods has large influence on the welding quality. In this paper, we take the GTAW of small-diameter pipeline as an example to analyze the effect of three welding methods on the appearance forming of weld pass and the welding quality, and to summarize an appropriate method during the site-welding of pipelines. Therefore, the pass rate of site-welding of pressure pipelines was increased.