Abstract: Statistical analysis was carried out on welding defects type of low carbon bainite steel WDB620 adopting shielded metal arc welding and gas shielded arc welding methods at different thickness.Through t-test,it is found that there is no marked qualitative difference in welding defects type between shielded metal arc welding and gas shielded arc welding.But the productive efficiency adopting gas shielded arc welding is greater than adopting shielded metal arc welding.So if possible,gas shielded arc welding method is recommended for low carbon bainite steel WDB620.