Abstract: The shape and current density of current-carrying region in constricting TIG arc with insulating sheet were analyzed by the low disturbance electrostatic probe. The floating potential and ion saturation current of probe were obtained separately in sections at different location along arc axial direction. The results show that the insulating sheet is over the arc root to make the arc not be constricted; with the constriction of insulating sheet, the current-carrying region pinches in the direction of constriction and potential gradient increase. When the constriction effect on arc root is intensified, both of the current density and temperature of current-carrying region are enhanced, and the heat is much moreconcentrated near the center of current-carrying region section.