Abstract: Aiming at the improvement of arc stability in low current TIG, a power supply which could supply direct current superposed high-frequency pulse current was developed. By testing waveform of output current and collecting arc morphology with a high-speed photography system, small current arc characteristics and influence of DC superposed high-frequency pulse on extremely small current arc and 6 mm gap micro-arc were studied. Forming causes of micro-TIG arc characteristics and high-frequency pulse effect were discussed. The results showed that the power supply could rapidly transform, and it had characteristics of high accuracy and stable output. As the current decreased, arc morphology changed and did not remain “bell-shaped”. High-frequency pulse current could improve stability of micro-TIG arc, so that the arc could maintain stable combustion when the average current was as low as 2 A. When the arc length reached 6 mm, 8 A micro-TIG arc would experience a large morphology variation, and high-frequency pulse could reduce its amplitude of variation and improve arc stiffness.