The　electrical　property　and　microstructure　of　SrTiO3　capacitor-varistor　ceramics　sintered　in　different　atmospheres　were　investigated　in　the　present　study.　The　electrical　experimental　results　show　that　samples　sintered　in　strong　reducing　atmosphere　of　25%N-2+75%H-2　and　heat-treated　in　air　have　a　low-resistive　core　with　a　high-resistive　surface　layer　around　it,　which　is　named　surface　effect　The　XPS　results　reveal　that　surface　effect　results　from　the　diffusion　process　of　oxygen　during　hear-treatment.