The failure characteristics of the contact material Ag-SnO2 were investigated by X-ray diffraction (XRD),scanning electron microscopy (SEM),and X-ray energy dispersive spectroscopy (EDS).Phase analysis showed that there were Ag,SnO2,and Sn on the contact surfaces at the time of failure under the load condition of 30 A and 220 V (AC),which means that SnO2 decomposed in service.When the contacts were tested under airproof ambient condition,half-spherical bulges came into heing on the contact surfaces,which resulted in early failure and dispersive characteristics.But half-spherical bulges were not found when the contacts were tested under open ambient condition.The temperature change of the contacts during the life testing under airproof ambient condition was different from that under open ambient condition.