Abstract: This paper mainly introduces the electrical characteristics (static and dynamic) of the Robot MOSFET Arc Welding Invertor and its arc welding technological properties. Emphases are laid on the analyses of the current and voltage wavefonns of the main circuit as well as the energy loss of the MOSFETs. The different static characteristic curves and parameters of electrical reactance are also discussed. The experimental results show that this new type invertor can improve the adaptability of the weldng robot, and makes less spatter during arc welding.