Residual distortion is a serious problem associated with welding thin aluminum alloy plates. As a distortion control technique static thermal tensioning has been used for many years. Owing to the insufficient understanding of its control mechanism and parameter influence, its application cannot always yield ideal results. So finite element analysis was performed. Based on the simulation results, presetting a saddle-shaped temperature field during welding can significantly reduce longitudinal inherent shrinkage strain in the weld and its adjacent zones, which will then reduce residual stresses and distortion. Temperature difference between the side and central zones is a key parameter and with its increase distortion reduction can be improved. Postweld thermal tensioning can cause certain plastic tensioning, but its effect cannot compare to that of a preset one. These numerical simulation findings were verified finally by experimental investigation.