Abstract: The voltage-current characteristic and thermal efficiency of a plasma gun are key factors influencing the quality of the plasma spraying process. The electric and thermal characteristics of the newly developed micro-plasma torch were investigated. As one of the factors effecting the plasma arc voltage, gas injection was also researched in this paper. The plasma arc voltage for the radial injection mode is much lower than that of axial injection mode and the integrated mode. However, the currentvoltage characteristics of the plasma jet show a decreasing tendency in spite of the three gas injection modes. With the integrated mode, stable and long plasma jet with high heat energy was obtained. The thermal efficiency of the micro-plasma gun ranges from 56% to 76%, and the plasma enthalpy is 3.28 kJ/g~11.16 kJ/g. With designed special plasma gun structure and integrated gas injection mode, the plasma gun shows a high thermal efficiency and plasma enthalpy which is suitable for the coating preparation with high qualities.