Abstract: Through analyzing the arc shape and testing the influence of the fluctuation of arc length on the dispersion of arc current and weld width.the authors put forward that the TIG welding power source with compensating energy could make the heat input into the workpiece constant under the fluctuation of arc length.A mathematical models based on technological experiments of the thin sheet TIG Welding(TSTIGW) was established and the TIG welding power source with compensating energy controlled by 8098 single chip microcomputer was studied in the paper.