Abstract: Numerical simulation calculation of TIG welding of thin wall aluminum cylinder by the thermo-elastic FEM has been conducted.Based on the generating of analysis model,the values and distribution at the centre of weld seam for transverse tensile stress and strain produced by pre-tension upon the solidification metal at the back of molten pool.Experiments were performed to verify the simulation results.It can be drawn that,for weld metal just solidified at the joint pre-tension load can produce transverse tensile stress,which increases the tendency of welding hot cracks.And with the increasing of pre-tension load,the transverse tensile stress increases.When the pre-tension stress is 60,120,150 and 210 MPa,the crack length in specimens is 5.2 mm、8.1 mm、8.9 mm and 10.6 mm,respectively.The tests results indicates the reliability of simulation results.