The arc evolution and cathode spots of nanocomposite Ag-SnO2,Fe-doped nanocomposite Ag-SnO2 and commercial Ag-SnO2-In2O3 contact alloys were researched by high-speed camera and scanning electron microscopy(SEM).Experimental results show that the evolution of arc discharge in air can be divided into three stages:arc forming,steady burning of arc and attenuation.Compared with commercial Ag-SnO2-In2O3,after Fe doping,nanocomposite Ag-SnO2 contact has double time of arc forming and shorter time of steady burning.It also has more cathode spots corresponding arc roots which jump fast and have a larger motion region on the contact surfaces,as a result of the time of arc roots stay on the contact surfaces is shorter,and therefore the heat stream input cathode spots is decreased.After arc burning,the cathode spots are dispersive and melt is lighter,showing better characteristic of erosion resistant to arc.