The CMT seam welding parameters of Q345 NQR2 weathering steel sheet are optimized by three-level five-factor interactive orthogonal experiments. Ten typical positions of 18 groups of experiments were scanned by a three-dimensional scanner,and the optimal welding parameters were obtained by deformation analysis. The effects of welding factors and interaction effects on deformation were analyzed by visual range and variance analysis method. The result shows that the welding gap and the interaction between wire feed rate and welding speed are the key factors affecting CMT seam welding deformation of Q345 NQR2 weathering steel sheets. The welding deformation of Q345 NQR2 weathering steel sheets can be effectively controlled by adjusting wire feed rate,welding speed and welding gap.