The technology of automatic welding technology for long-distance pipeline has been widely used in long-distance pipeline welding as its fast welding speed,small groove angle and narrow welding surface. However,during the process of radiographic inspection（RT）welding seam,it is always puzzled by the linear images which are often mistaken for false defects. In this paper,carry out process evaluation tests and take comparison of unqualified RT samples. Finally,find that this kind of linear image is not a pseudo-defect,but a linear defect produced by edge incomplete fusion. According to the causes of the defect,we find out the solution to eliminate edge incomplete fusion,and improve the quality of long-distance pipeline automatic welding. The welding qualification rate can reach more than 98.5% by one pass welding.