Abstract: A three-dimentional solusion for heat conduction in an infinite plate of finite thickneses δ,with a Gaussian distributed moving heat source,was obtained for both DC and pulsed welding.Welds were made on 18-8 stainless steel of 1mm thick by both DC and pulsed TIG welding.Both calculated front and back side weld widths were compared with real one,and the average error is 4.92%.