A two-dimensional transient model is introduced to describe the heat transfer and fluid flow in pulsed gas tungsten arc (GTA) welding. The current continuity equation has been solved with the combined arc plasma - cathode system, independent of the assumption of the current density distribution on the cathode surface which was essential in previous studies of the arc plasma. The temperature distribution in pulsed GTA welding has been described, and the transition processes of temperature contours and current densities at the anode centre have been studied. Moreover, the effects of pulsed welding parameters on the dynamic process of current density at the anode centre are studied using the developed model. The results have been compared with experimental data measured by the probe method.