Welding distortions of large steel structures had mainly been estimated with some simplified formula obtainedby lots of experience and numerical analyses for small steel structures. However, the large structures wouldhave different characteristics of distortion with welding because of their own stiffness coming from the sizeitself. Therefore, in order to find some measures for preventing welding distortion of large structure, it isrequite in advance to precisely analysis thermal stress and distortion during welding of the structure. Numericalanalysis for larger structure has been known to take large amount of calculation time and have a poorconvergency problem during the thermo-elasto-plastic calculation. In this study, a hybrid method is proposed to analysis the thermal stress and distortion of a large steelplate with the finite element analysis by incorporating with temperature distribution of the plate calculatedby an analytical solution. The proposed method revealed that the thermo-mechanical analysis for welding ofthe large structure could be performed with a good convergence and produced precise results with muchreduced time consumption.