Abstract: In order to analyze the arc igniting course of the plasma-MIG (metal inert-gas) dual-arc welding, Paschen law was introduced to calculate the breakdown voltage on the different arc igniting paths.The effect of disruptive distance and temperature on the arc ignition was studied.The pattern that the plasma arc ignites by means of the breakdown path provided by the MIG arc was proved. It has been shown that the temperature and type of the shield gas must be taken into account when the lowest breakdown voltage on different igniting path was compared.Paschen law is suitable for analyzing the effect of these parameters, and can be used to predict the igniting path of the second arc.The method can also be used to other dual-arc welding method.Finally, the actual arc igniting course was observed and analyzed by high speed video camera.