Abstract: The improvement was made to solve the problems existing in present numerical models of fully-penetrated GTAW (gas tungsten arc welding)weld pool surface deformation.Based on the complete and correct equations of both top and back surfaces deformations of molten pool and the more accurately predicted weld pool geometry, the fully-penetrated molten pool surface deformation at the quasi-steady state were numerically calculated and discussed.The calculated results were verified by experiments.The results indicate that this study solves the problems of the lesser predicted molten pool surface deformation in literatures, and improves the numerical analysis precision of molten pool surface deformation.