Abstract: The deformation amount of the material during the seam-jointing process of the pipe blank with an opening has a significant impact on the geometric dimensions of the steel pipe. The seam-jointing process may cause defects of the pipe such as misalignment and pouting，which increases the difficulty of steel pipe jointing on the construction site. And the splashing as generated during the pre-welding process may damage the probe of the flaw detection equipment，and also compromise the appearance quality of the steel pipe. In order to reduce the defects as above mentioned and occurring in the pre-welding process of the LSAW pipe as well as pre-welding spatter and porosity，studies are conducted on the deformation amount and deformation law of the steel plate during the steel pipe jointing process，the principle of jointing of the pre-welding machine and pre-welding process specification，the relationship between the protective gas and the spatter amount，and the relationship between the welding specification and the weld penetration depth. As a result it is revealed that the adjustment of the pre-welding machine roller beam parameters is the key to the quality of the steel pipe seam-jointing，and the pre-welding spatter amount is increasing along with the increase of CO₂ proportion. The research result is worth of guiding workshop production type adjustment and improving quality of the pre-welding process technology.