Abstract: To meet the needs of the thin sheet circumferential TIG welding,a new control system based on the single chip microcomputer has been developed. The System has the following characteristics: (1) In welding sequence control, exclusive design rules have been used for manual operations and inclusive disign rules have been used for manual-automatic mixture operation. By this means the wrong actions of the system caused by interinfluencc in manual operations and between manual and automatic operations have been eliminated and the reliability of the system has been fully guaranteed. (2) New touchable arc starting technique has been developed and used in the system. The technique is not only without high choping frequency and high voltage arc starting pulses which can distirb and destroy electronic circuits, but also dependable in arc starting and little pollution on tungsten electrode and workpiece. (3) The arc length control of the System is based on the principal of statistics. It makes the system excellent in control performance, simple in electronic circuit and strong in disturbance resistance.