The　objective　of　this　paper　is　to　determinate　the　influence　of　grading　capacitance　on　breakdown　characteristics　of　a　double-break　vacuum　interrupter.　A　prototype　of　double-break　vacuum　interrupter　was　built　up　as　a　U-type　configuration　with　two　12　kV　vacuum　interrupters　in　series.　The　double-break　vacuum　interrupter　is　stressed　by　a　power　frequency　withstand　voltage　and　a　lightning　impulse　withstand　voltage,　respectively.　The　lightning　impulse　breakdown　voltage　U-50　is　obtained　by　an　up-and-down　method.　Five　grading　capacitance　are　designed.　One　is　with　no　grading　capacitors,　which　is　as　a　benchmark.　The　other　four　capacitances　are　100　pF,　500　pF,　1500　pF,　and　10　nF,　respectively.　The　experimental　results　show　that　there　is　an　optimum　grading　capacitance　which　leads　to　a　maximum　impulse　breakdown　voltage.　As　the　grading　capacitance　increases,　the　number　of　successive　breakdown　increases　when　breakdown　occurs.　With　grading　capacitance　increasing,　the　power　frequency　breakdown　voltage　increases　and　finally　reaches　saturation.