Abstract: Soft-switching is the key technology to improve the reliability of inverter arc welding power.A new design of soft-switching inverter arc welding power is proposed in this paper.The soft-switching state of any load,such as unloading,short circuiting and arcing,can be primarily realized by the design.The paper analyses the relation between the parallel capacities and the shutting loss of the leading-arm,the effect of the serial capacities and the inductance of the loop impact on the change of current during the circumfluence time,the zero current shutting extent of the lagging arm and the ZVS,ZCS condition of the leading-arm devices and lagging arm devices.In order to solve the problem that the soft-switching will fail during unload or light load peried,the anthors put forward a layout introducing no-power current sect and several primary resonant parameters.Practice shows that the design reduces the switching stress and loss,improves the reliability of the whole machine and reduces the cost of the arc welding power.