Abstract: As the internal and external spiral welded seams showed different space distributions, it inevitably caused their different projective positions after being irradiated by X-Ray. When judging the off-seam of the spiral double submerged arc welded pipes seam by what used for common flat double seam, it would certainly result in big deviations with the real situation. Through theoretical analysis and calculation, the paper detailed the reasons of the deviation and proposed ways to prevent it. Current studies might have a real reference value in judging the off-seam of the spiral double submerged arc welded pipes seam.