Abstract: The effects of distortion control in welding thin aluminum alloy plates by two kinds of thermal tensioning were investigated.It is shown that the effect of dynamic thermal tensioning by trailing intensive cooling is greatly influenced by the heat-dissipating conditions of the fixtures.Without uniform preheating it is difficult for trailing intensive cooling alone to create a saddle-shaped temperature field and the mechanism of reducing distortion is equivalent to the decrease of welding heat input. While combined with uniform preheating,dynamic thermal tensioning comes into being to some degree and the effect of reducing distortion increases obviously.Static thermal tentioning can create a remarkable saddle-shaped temperature field and reduce welding distortion effectively.The minimum welding distortion was obtained by the combination of static and dynamic thermal tensioning.