Abstract: The characteristics of constraint force and dynamic welding distortion of aluminum alloy 5A12 with constraint TIG welding were investigated by dynamic temperature and distortion measuring system.The effects of constraint force and its release on out-of-plane welding distortion were analyzed.Research results show that out-of-plane welding distortion is different with the different constraint force,and welding distortion can be controlled by the proper constraint force.the welding distortion will rebound to some extent after the constraint force being released,which is the main factor to result in the residual distortion of constraint welding;the residual distortion of 6 mm thick aluminum alloy 5A12 plate can be well restrained at the constraint force of 0.2 kN,and the loading position is 45 mm form the centerline of weld.