Abstract: Some welding defects of the LSAW pipe are analyzed to find out the causes for such problems as arcbreaking,poor weld seam-shape quality,slag-inclusion of inner weld seam and weld seam under cut,etc.It is identified via the analysis that the fluctuation of the wire feeding speed is the main cause for the above mentioned problems.Accordingly certain components and parts of the wire-feeding system are modified or replaced to eliminate the fluctuation of the wire-feeding speed,and get the wire-feeding speed and welding wire melting speed well balanced so as to ensure the stability of both the welding process and the welding quality.The requirement for the welding wire quality,and cautions for operation of the wire-feeding system are put forward.