Abstract: In order to study the distribution rule of residual stress of AZ31B magnesium alloy weld, The MSC.Mar was used to make a numerical simulation analysis of temperature, residual stress and strain field of DE-GMAW welding a circumferential weld of a diameter 200 mm, 6 mm thick magnesium alloy cylincle. It was found that the residual stress on weld and heat affected zone is larger, and gradually decreases away from the weld center. The longitudinal residual stress is greater than the transverse residual stress in most areas, but not include the most outside and inside weld areas. These results provide theoretical knowledge for the control of welding residual stress of magnesium alloy.