In this paper, a moving heat source model based on Goldak's double-ellipsoid heat flux distribution is presented. A C++ programme was developed in order to implement heat inputs into finite element thermal simulation of the plate butt joint welding. The transient temperature distributions and temperature variations of the welded plates during welding were predicted and the fusion zone and heat affected zone were obtained. Effects of the heat source distribution, energy input and welding speed on temperature changes were further investigated. (c) 2005 Elsevier B.V. All rights reserved.