Abstract: On the basis of mathematical moduels and experiments of the Thin Sheet TIG welding,TIG welding power supply with effective heat power constantly controlled by 8098 monolithic microcomputer is studied in the thesis.The power supply which can present variable linear Volt-Amper characteristic(VAC)at an angle ranging between 70°and 145°is able to give the optimun VAC by means of user's pre-trial.With the system,the equivalent weld width is stable when the variation of arc length is no more than 5 mm and the fluctuation of grid voltage no more than ±10%.