Abstract: For understanding the character of TIG arc current-carrying region and ascertaining the range of current-carrying region, a low-disturbing electrostatic probe was developed to measure the potential of probe in floating condition and the current of probe with bias voltage in various sections along the axial direction of arc. The results show that it can get the ion saturated current by probe with negative bias voltage and the electron saturated current by probe with positive bias voltage. And then the half widths of the ion saturated current peak and the electron saturated current peak can represent the radius of current-carrying region and arc including peripheral negative ion region respectively. Both of the range of current-carrying region and arc increase into widest near anode from cathode to anode along the axial direction of arc. In addition, it is found that the effect on probe caused by peripheral negative ion region of arc can reduce the potential of probe in floating condition. This effect can be neglected when the exposed length is decreased into 5-6 mm.