Abstract: The characteristics of dynamic welding angular distortions of aluminum alloy 5A12 with TIG welding are investigated by self-made welding dynamic temperature and distortion measuring system.With analyzing thewelding thermal cy cle and dynamic angular distortion curves, two characteristic values, the down warping maximum point and warping balanced point are put forward to describe the dynamic curve behavior.The changing rules of the dynamic curves under different welding parameters are investigated by means of orthogonal experiment method.Based on the results, mathematic model on the dynamic angular distortion curve is introduced. The results show the dynamic angular distortion can be expressed by the mathematic formula accurately.The down warping maximum point, warping balanced point and the slops of the curves are the key factors that characterize the dynamic angular distortion curves.