A miniaturized argon arc running at maximum current 45 A and pressure 1.75 × 105 Pa with a differential pumping interface unit has been developed. The measurement in UV and VUV range indicated that the stability, both short term and long term, and reproducibility of the spectral radiance of the mini-arc were better than ±0.5% and the similarity among mini-arcs was better than ±1%. The theoretical calculation of the spectral radiance of the mini-arc based on Hofsaess theory agrees with the measurement results within 10%. Richter method was used to carry on the plasma diagnostics of the mini-arc. The results show that the argon plasma temperature is 12650 K and the electron density is 1.29×1017 cm-3 when the current of the mini-arc is kept at 40 A and the pressure at 1.75×l05Pa.