A theoretical and experimental study of heat flow distribution during the autogenous GTA welding of metal plates is made. The theoretical part of this study involves the development of a numerical model based on a finite-difference implicit-solution method for the transient three-dimensional heat conduction equation with a moving heat source/sink, which simulates the welding process. The experimental part of this study involves the measurement of temperature distribution in the welding workpieces. These experimental results are compared with the numerical ones and the agreement is fairly good. The numerical solution developed is easier and more accurate for studying the effect of many welding parameters on heat flow distribution, the welding speed, the input-heat energy and the type and geometry of welding workpieces.