Abstract: The welding stress and deformation of GMAW automatic welding that was the key in deep-water offshore pipeline laying were researched,which had process features of without backing,narrow groove and transverse welding. On the basis of theoretical analysis of welding stress and deformation,the average thermal cycle curve of weld cross-section was extracted as the loading heat source of multi-pass welding with SYSWELD software as a tool,Numerical simulation of multi-pass welding deformation and stress distribution of API X65 plate with the same pipe thickness and groove parameters was carried out,and a transverse automatic welding test system was set up for multi-pass welding verification. The results showed that the numerical simulation results of the final welding deformation were in good agreement with the experimental results,and the errors between them were mainly due to heat flow distribution,calculation accuracy of the two-dimensional cross-section model,constraints and the characteristics of the thermal cycle curve. In the process of multi-pass welding,the first few layers of welds had great influence on the final welding deformation,while the latter few layers of welds have little influence,which was due to the large basic deformation in the first few layers of welding,and the deformation compensation caused by the release of residual stress in the latter few layers of welding obviously offset a part of the welding deformation.