Abstract: The arc electrical signals were collected the data acquisition system in the plasma-MIG welding process, and the U-t、It、U-I diagrams analyzed with the Labview software were obtained. The difference of arc characteristic between plasma-MIG arc and MIG arcwas studied and the effect of increase of MIG current on the electric signals of the Plasma-MIG arc was analyzed. The unstable arc electrical signals of Plasma-MIG were gathered and the result indicates that some contacts exist between inner arc and outer arc.