A three dimensional mathematical model was developed to research the dynamic interaction between energy propagation and keyhole evolution in PAW (Plasma Arc Welding). Particularly, a keyhole-tracking heat source model was proposed to reflect the energy propagation in the wake of keyhole evolution, which was tracked by the VOF (Volume of Fluid) technique. The model consists of a Gaussian heat flux on top surface and a lower developing conical heat source related to the dynamic keyhole growth. In addition, a dynamic energy distribution coefficient was established, bound up with the keyholing process for the first time. The design of this heat transfer model introduces the analogy to actual energy propagation in experiment. Evolution of the dynamic energy density distribution concerning keyhole effect was analyzed in details, and the corresponding temperature field was calculated and displayed to reveal the mechanism of thermal process in the workpiece. Furthermore, the keyholing process and molten metal flow in the weld pool were investigated to exhibit how the keyhole promotes the deep penetration welding. Finally, the experiments were carried out on the stainless steel plate, and the measured weld bead geometry, keyhole size and time for workpiece completely penetrated through were all close to simulation results. (C) 2013 Elsevier Ltd. All rights reserved.