Abstract: Numerical simulation analysis model for gas metal arc welding(GMAW) was created in the course of the welding heat based on Visual Fortran.A double ellipsoid heat source mode was adopted to depict the distribution of a moving GMAW arc.Transient variations of weld pool geometry and free surfaces deformation were predicted and verified.The results show that the calculated width and depth of molten pool are in agreement with those of the experimental results.