The weld pool convection and the bead formation in a gas metal arc welding were simulated by a three-dimensional incompressible smoothed particle hydrodynamics method. Moreover, the ensemble average processing was carried out to investigate dynamic changes of the velocity field of a weld pool. From these results, it was formed that the droplet transfer affected the velocity field of the weld pool, especially the region which was about 3 mm from a weld pool surface in the vertical direction and about +/- 5 mm from center of the heat source in the horizontal direction. (C) 2018 Elsevier Ltd. All rights reserved.