Abstract: The VPPA-1 welding power with 80C196KC MCU as the control center and double invert topological structure as the main circuit was prepared.Arc stability mechanism and control methods of VPPA were studied.The re-ignition principle after the zero passage at low current and the arc stability of VPPA in largescale welding conditions were analyzed principally.It is proposed that zero passage should be enhanced before the positive electrode becomes negative electrode by program enactment at low current to control the stability.However, in the large-scalewelding conditions, the arc stability is controlled by zero passage.It is helpful for the arc properties and welding process control in VPPA welding.