Abstract: It is of considerable practical interest to understand quantitively the heat and fluid flow phenomena in welding molten pools. The purpose of this paper is to develop a mathematical model to evaluate the three-dimensional fluid flow and temperature profile in a moving TIG welding molten pool. The model considers both the fluid convection-conduction heat flow in the pool and the conduction heat transfer in the surrounding solid material so that the limitations of the application of Rykalin's formula and the numerical method of pure conduction could be avoided and the scope of the previous two-dimensional method for stationary arc extended. The theoretical predictions based on this model are found to be in good agreement with the experimental measurements.