The forming process and dynamic behaviors of droplets in gas metal arc welding (GMAW) were numerically simulated by using weak electromagnetic coupling method, with considering the gravity, the electromagnetic force, the free surface and the turbulent flow in the droplets. The shape update of the droplets was calculated on basis of VOF and CSF theories. The Gaussian electric current density was identified as boundary conditions for calculating electromagnetic force. A weak electromagnetic coupling model was used to study the characteristics of relevant physical variables and their roles in metal transfer. The simulation results suggest that the maximal value of electric current density lies in the neck of droplets, and the electromagnetic force has great effects of accelerating droplets’ contraction and shortening their falling time. Under the action of strong electromagnetic force, the metal transfer is in a spray form rather than a globular one in GMAW process. The simulated results agree well with theoretical analyses and predecessors’ experiments.