In order to improve the control precision of welding current and the stability of arc with low current du-ring the micro arc welding，a precision inverter power supply is designed． In this power supply，a digital control system based on the digital signal processor is introduced into the traditional argon tungsten arc welding inverter，and the limited bipolar control method is used to realize the soft switching of the full-bridge inverter． In addition，the electrical characteristics of the arc load are introduced，the requirements of welding process for the power su-pply are analyzed，two kinds of waveform control schemes respectively for direct current and pulse are designed，and the software procedure of the power system and the corresponding control algorithm are expounded． It is de-monstrated that both the precise control of output energy and the nice consistency of waveforms can be achieved by accurately controlling such output parameters as current，time，frequency and pulse width; and that the integral separation PID control algorithm helps to realize a smooth transition of the arc from arcing to breakdown and then to annihilation，thus improving the stability of arc with low current．