Abstract: A heat flux distribution model of arc which suits for large surface deformation of GMAW weld pool is given in this paper. Based on this model and the consideration of droplet transfer process and the weld reinforcement, a numerical analysis model of welding heat flow field and a calculating program are developed. By numerical simulation, the interactions of welding process parameters, GMAW weld pool surface deformation, arc heat flux distribution, weld pool geometry and temperature profiles are quantitatively analyzed. The experiment results show that compared with the Gaussian model of arc heat flux, the heat flux distribution model of GMAW arc given in this paper accords with practical situation much beffer.